That's your first love Seo-In and you still love him. You want him only for you. That's it. Don't be in denial just confess already. But I think he will be more possessive if they will be exclusively dating.
Both of you just be honest and confess.
Though I'm curious with Taegu's POV as well. (โฐหโกหโฐ)
No man, you're not helping him by saying yes every time Taka acts like this. He needs mental help.
Yu loves the guy so โฅ๏นโฅ
Hey Kotani explain yourself why. We need your POV to understand your words. Because those are painful words to tell your partner if marriage is possible between the two of you.