I wouldn't say he was ever sexually assaulted. He consented to everything. Light coercion, perhaps, but he didn't mind it at all. I don't think he really has strong feelings towards anything, really. I do think he's always liked Jeong though.
Coercion tends to lead BL relationships in Asian cultures because it's not legal in most Asian countries.
And Jeong is allowed to feel disappointment because he really wanted the two of them to be a "natural" Alpha/Omega pairing.
He only agreed to it because he was being MANIPULATED thinking Jeong was helping him, so yes it does fall into the category of sexual coercion. And that's the thing, he is NOT ALLOWED to because even the person himself is fine with his secondary gender. Dongha's body is his. So his feelings matter the most. Besides, it's not like he can't date Dongha because he was a beta, he just took the creepiest way to court him. Liking this story doesn't mean you have to justify what he did
As much as I don't mind since it's fiction, this type of mindset where you start justifying it it's really harmful to yourself and SA victims, please don't try to justify it, what he did was wrong and it's SA. Don't try to explain or justify these behaviours, if you enjoyed it or didn't mind you have to be very conscious that NONE of this can be justified and it's absolutely wrong fo do
You having big feelings about how he feels is literally the same thing. You can't control how someone else feels about something.
Feelings themselves aren't wrong. It's what we do with those feelings and the actions that are taken after feeling them that matter.
Like how he IMMEDIATELY corrected himself because he realized that any sign of being disappointed could definitely hurt his friend. If anything, he OVER-corrected by saying stupid stuff like how he didn't like omegas anyway, and trying to hypnotize himself into only liking betas since his crush was a beta at the time.

Aside from the obvious SA and manipulation, I guess what's rubbing me the wrong way is how disappointed he looked when Dongha didn't manifest as an omega after the first test like he'd expected, like what right does he have to feel that way when Dongha himself didn't have a problem with that