I mean I think it's fine to not understand, it just means you're a different person and don't have the same experiences.
When a person has been abused/neglected their entire life and don't know anything different, when someone's been dangling something they want in front of them without truly giving it (a promise of love or security), it's easy to get tunnel vision. It becomes the only thing that matters. And in this case having self respect is a luxury because this is the way Sejin has learned to survive.
I've not had it that bad myself, but I can kinda understand both your side and Sejin's. I've never been desperate for affection to the point of committing criminal acts or betraying someone's trust like that but if things were worse for me I could see how it could get there. But I've also had the same coping mechanism as you after feeling really badly hurt and abandoned, when doing everything for a person who didn't want me didn't work out great for me. I never wanted to feel that pain again, so it was easier to run at the first sight of trouble. But I think I could react that way because I had some base level of security. If that makes sense?
Sorry for the long reply! I wish you all the best, I know cutting ties first isn't always the easiest coping mechanism to have either.
What Sejin has is abandonment issues or anxiety, you have it too (in fact everyone has it to varying degrees) but your coping strategy as you said is quite different from Sejin. In a similar situation, you'd probably be independent and emotionally detached, while Sejin would be dependent and sensitive to emotions. Anyways, I guess your defense mechanism is much better, since you have more freedom at least.
i get it! altho i DID do both lol. First, when i was really young up to my highschool years, I cared deeply abt everything my loved ones thought of me. Then I got so sick and depressed of losing myself over and over again and did the latter all throughout college until now. (it's not that bad now). sometimes i think it really depends on the situation, you now? like sejin was abandoned his entire life, even in the oresence of another. and maybe guilt and gratefulness play a role too. Neways! Hope you're doing okay!

I feel like I have a hard time understanding wanting approval and affection so much that you’d do what the omega is contemplating. My defense mechanism is throwing away the relationship before they throw me away lol. If my husband cheated on me, I’m gone. My parents want to disown me? I’ll disown them first.
Both are probably toxic coping mechanisms of course.