Don't know how bad the alpha is. That remains to be seen. As far as threatening to take the kid away?? Noah is the one under for whatever reason his the fact he is the omega who had forced Ian into a mate bond against his will, whether accidentally not knowing he had turned into an omega, or willfully, knowingly. And if he had been a beta he wouldn't have gotten pregnant when alpha releases inside him. The heat...was induced during Ian's rut, most probably. So Ian is pissed some random omega marked him (well, he did the marking but same deal) and ran away. He didn't know who it was. And then he prob figured out that maybe YeJun had turned and then went looking for him. YeJun hid THEIR kid away. So far as we have seen there is no reason for Noah to have done that
I'll never understand how can anyone be legit blamed for something they didn't have control over at all lol. You bet if Yejun knew he's an omega, he wouldn't have f-ed with this ahole.
And to answer you, why he would shut up about the kid: usually there's a fear of losing the child to the wealthy partner who has more resources to win a court case against the other parent. Also, it's heavily suggested how Mr. Ahole got interested in toying with Yejun _because_ he was supposed to be a beta, so he wouldn't get him preggo, but at the same time could f around all he wanted with Yejun. It was a convenience thing as far as we know the story so far. So how would it be viewed if Yejun confessed a pregnancy? Gold-digging, tying down Mr. Ahole with the kid, going after his money. He most probably would have received accusation after accusation. I would shut the hell up as well if this happened to me, and would go for a quiet, simple life raising my kid. There's no legal obligation to tell the father they'll become a dad, especially if said individual gives off such heavy indirect signs of only playing around and preying on others. From a moral pov yes, Yejun _could_ have informed him, but I completely understand why he chose not to. This ahole's first thing to do was to dominate him with pheromones, separate Yejun from the kid, and f him. This is in no way a comprehensible behavior even if he's mad. If he was so bothered by this, as they said, it's illegal to mark others just like that, so then go make a court case out of it, but don't toy around with the man.
TLDR No, I don't agree with you, this alpha is f-ed up bad and behaves in a disgusting way intentionally, while Yejun's marking was completely out of his hand as he didn't even know he's an omega, so let's not blame him for this. He lived with the thought of being a _beta_ my man, it's not even the case he knew about the recessive trait and tried his luck. He. Didn't. Know. He's. An Omega. Period. This mofo knows very well, what's he doing, and that it's wrong af. L alpha
I agree with you regarding his using the pheromones to suppress him is an asshole move. And let's just say for the sake of the argument that he is an alpha asshole to settle that. But of course, in the past he wouldn't have been able to do that because Noah/YeJun was immune to that. IF he was THAT much of an asshole he probably WOULD have preferred an omega, so that he COULD use his hormones to subjegate the omega. Why mess around with a beta for???
~ANYWAYS~
What I want to get the crux of is this:
They had a very good friendship relationship UP until their very first sexual intimacy that we can see in the latest chapter. (Ch. 7). In no way did it depict him as being an asshole. Let's say he DID seduce the beta, then you can say then that beta had been seduced. The problem for YeJun lies in the fact that he has feelings for DoYoon so he went along with him. Let's SAY for the sake of the argument that DY seduced YJ KNOWING YJ has feelings for him, then yes, he's an asshole for using him, and NOT RECIPROCATING those feelings. YeJun could have easily denied him, but because he has feelings for the alpha he decided to go along with it, As He HIMSELF had said...
So this relationship is based on what would SEEM to be a one-sided relationship. AT "ANY GIVEN POINT IN TIME" YeJun COULD Have said "let's quit this". It doesn't have to be DoYoon to be the one breaking it off. The reason the beta is hurt is because he's the one with more emotional investment. And another thing, if sex with a beta is SoOO painful or frustrating because of how a beta isn't built to take-in an alpha's dick, why can't DY just do it with an omega?!? Did you also miss the part where he'd asked YeJun if he'd wanted to stop before he puts it in the first time around?!? And then instead of thrusting in all-the-way he only went as far as they both could handle and then he said, ok that's enough for today. Let's say again, for the sake of the argument that he's only SLOWLY easing the beta into the sex so he won't feel so much pain and will be less likely to refuse him and build more trust with him, then you can say, oh, he's only doing this for that purpose: getting laid without worrying about the pregnancy. We ACTUALLY DON'T know the reason why he'd said what he'd said....it can be he was just saying that to comfort YeJun, OR he has his own hangups about omegas, maybe, as someone else had said, he wanted a pure relationship NOT dictated by pheromones (but which, for some unknown reason, you happen to conjecture but is not a fact that he wants to mess around w/o consequences). He must have broken it off with YeJun because he had been mate bonded. The reason was NEVER given.
Also, during the rut we don't know if it was an accidental marking due to an unawareness of omegahood manifestation and subsequent heat induction by a rutting alpha or if YeJun went into it knowing he's been turned...these are all assumptions.
All-right-now, we're going on to the court cases/parental rights. BOTH parents have rights to the custody of their child. Noah doesn't have to the right to keep the child solely for himself, unless he's proven incapable, which he isn't, but if the lawyers are involved ofc the alpha would win. Now, so far, we have ONLY been seeing things from a sopping wet mop of a sorry-ass omega who is fearful of the repercussions of having marked an alpha and then running away, AND WHO for some UNKNOWN reason, is raising the child IN SECRECY AND FEARING that child would be taken away. Nobody had explained the reason why that is. Is this a typical setting in this universe?!? First of all, DoYoon was never even interested in Omegas in the first place, OR that he liked YJ regardless of his gender. When he came to meet/confront YJ, he had said, oh, yes, a child, he must be the right age to be mine. But NO WHERE did it say that he will LITERALLY be taking the child away. THAT is ONLY YeJun's fear - and again, I have no idea where his fear is coming from. I do not know whether or not YeJun is responsible for the marking or if it were accidental <--- but which MAY be the root of his fears.
If YeJun had interpreted DoYoon's saying that "it's good that you're a beta, and in fact it's good that you're not an omega" as saying that he's only worthy of DY if he is NOT an omega then his having turned omega makes him sad and scared that DoYoon will no longer be into him then it hurts him because he's afraid of being rejected. Who knows if he had manifested and sneaked in during DoYoon's heat while knowing he had manifested, hid the fact he had manifested and still had sex anyway, resulting in the marking OR that during DY's rut he went into heat not knowing he had turned. Furthermore, you can see YeJun is WAY more Lucid than DY was during the rutting sex, even though he was in heat. He even recovered first and went to wash the sheets. I'm ASSUMING he had more awareness about the marking than DY did. He's afraid and ran away from the responsibility of the marking AND the fact he's turned an omega, which MAY enrage DY or causes him to not like him anymore. Anyways, he was the one who ran away.
IF their relationship was purely FWB the only one to get hurt is the one with feelings. For the sake of the argument, let's say DY was just playing with him, then, end of story. But if DY had feelings but never expressed them then who knows?!? OR, that if he DOESN'T KNOW YJ's FEELINGS for him and YJ didn't express anything then yeah, it's all on YJ for not voicing his feelings. YJ went into this relationship WITH feelings. Nobody forced him into it. Even IF DY had broken it off for legitimate reasons he would still have been Hurt.
If DY didn't care about YJ why did he have sex with him?!? I mean, when they reunited?!? He could have just taken the child and go. No need to build any kind of relationship...my guess is that YJ DID such a good job of disappearing that it was difficult to find him. AND IF this Omegaverse is one that has betas manifesting into their second gender at some point in time other than during adolescence, at a MUCH later stage, or being w/ an alpha turns them... then the possibility that this may be the case came to DY MUCH LATER that his mate COULD be YJ, in which case then it can partially be attributed to the time lapse. We don't know. The other factor is that YJ hid well too. And so added to that it took him 5 years to find him. Just a guess. Since, 5 years is a very long time. If it hadn't occured to DY that maybe YJ had turned he wouldn't have tried to seek him out.
And like I said, if sex with a beta was so difficult and painful, as DY had said: "back then, even with a good amount of lube it was difficult" to insert and have sex and he couldn't thrust in all-the-way. My guess is that he likes YJ but either unvoiced or just an undefined or just FWB relationship. But when DY had cut it off, he didn't cut off the Friendship part, when I looked back it feels as if he cut off the sex part but wants to or wouldn't mind? with being friends. But YJ interpreted it as if DY doesn't want him anymore so he's heart broken. And he said he's been dumped, but for one to be dumped it has to be an official relationship (dating/bf/fiance). FWB doesn't have that same commitment and definition. As far as I know, it's not an obligation - you just stop being FWB once you decide you don't want to anymore, although that is the same for official relationships, but the one butt hurt is YJ, because he's the one with feelings, AT LEAST, as far as it has been shown.
I'm guessing he left because of a broken heart. Then he hid because he's fearful that DY would find out he's the omega that's he's marked, and according to what we know DY said to YJ that he doesn't mind that YJ is a beta, but we don't know the meaning behind that. Your assumption is that DY is 1) just playing around w/ YJ. Ok, so let's say he is, so what?!? 2) he's doing it so he doesn't impregnate some omega <--- Ok, but that is JUST an assumption!!! Now, the third point: why is he fearful the alpha would take away THEIR kid?!? It's the WHY for me. Not the legality of the case or how powerful an alpha's status is that can force the omega to relinquish the child.
ALSO, why would you ASSUME THAT "Mr. A-Hole" would think that YeJun did that to tie him down with money?!? Maybe with love, but not with money....in WHICH PART of the story did that even occur?!? You're trying to THINK INSIDE of DY's head when that is probably NOT the case...DY didn't approach YJ SOLELY BECAUSE he's a beta. He said it's better that you're a beta, but it never said why. Upon their reunion DY even said, I don't mind the marking, it even stabilized my rut. And WHERE did it say that DY thinks omegas would tie him down in that way?!? And IF SO why would he come after his child now?!? Assuming he knows about the child. Anyways, too much assumptions on your part. I'm leaving room for interpretations.
And let's say even if "tied down with a kid" he's wealthy enough...and can always, as you say, take custody of the kid and just tell the omega to "shoo" since he's powerful enough.
And...why would he care to go to court against YJ for the marking?!? What would he gain by it?!? Just wastes his time and money.
Can't you see HOW EXCITED he is to see YJ?!? He said, "NOW SEX with you is SOOO good, Cuz No Matter HOW MUCH lube I used in the past it would always be so tight".
And...during the sex he sniffed the omega, saying ~Ah~ "Oh yes, this is the scent I remembered". . The end.
If there are further discussions on plot points you want to discuss, feel free. I analyze everything, no jumping to conclusions just yet. Gotta wait to see how the story unfold.

So... gaslighting, stalking, kidnapping, rape, emotional abuse, manipulation... Yeah, let the seme go to Hell, like express, plz. The underhanded blackmail and threatening behavior with the kid is specially disgusting. F him big time, hope Yejun gets away from this dipshit at least for a few chapters.