spoilers:
Ml, Ex is just with the new guys because he accidentally slept with him
he felt responsible about doing that to the new boy so he had the urgency to stay with him. BUT he never actually loved his new BF, he still love his EX and still yearns for him
The reason why the new bF is too anxious is because he knows their relationship with the guy is not even rel. He was practically a stalker of the guy ever since college? or what ever he was stalking the guy but he was with ML that time.
so when ML disappeared he took the chance to be the new BF
The EX ML bf doesn't love the new BF he just feel obligated about what happened between them
This is just my personal opinion, but if Youngwoo is insecure about Joyoon being Taejoo's ex, then wouldnt that mean that Youngwoo's relationship with Taejoo currently is fragile and is held by a thin rope? I understand that theyve only been together for less than a year and for Joyoon to suddenly reappear again after being MIA for so long can cause some instability in the relationship. However, if you dont have enough faith in your partner and be childish towards his ex, then you just dont trust your bf enough. Personally, I just find those kinds of relationships pitiful and annoying.