Everyone is just too anxiouseven if it’s really Taegu who was there, it’s definitely about him accepting that his role in Yeongwoon’s life is done. He would still be by Yeongwoon’s side if he really needs help from him but for now he would just leave both Yeongwoon and Seoin alone and wouldn’t step into the line of their relationship.
Like you said, even if Taegu disapproves of their relationship and doesn’t want Yeongwoon to be with Seoin again(because he might get hurt again), he wouldn’t do anything to destroy their relationship because he respects Yeongwoon. If he really want Yeongwoon to not be with Seoin, he wouldn’t be really all nice to Seoin and even give him the files/hints about what Yeongwoon had gone through in the past 10 years.
We still need to be more focused on Haeyool. I don’t know why most of everyone forgot about Haeyool and more worried about Taegu…
Everyone really needs to calm down a bit!!

Firstly I think the creator has confirmed that the next chapters may be free on angst so let's relax. I'm seeing a theory that taegu may become the villian but I think it's haeyool. Regardless of his weird ass feelings taegu has some respect for yw that he would actually let it go. I think he was the one at the door and heard yw moaning and realized he and yw will never be and he left the bag. The one we should be worried about is haeyool. He is obsessed with yw and would use the redhead cousin to hurt yw for being with seoin and basically rejecting him. He seems unhinged considering how he was blackmailing yw.
I really hope we are given some fluff until further notice. I think the season will end with chapter one being revisited.