I get where you come from, but Taekyung is shown to actually be sure that he likes Haesoo and wants him. And Haesoo is easing into that right now. Joowon is still having trouble realizing his love that he subconsciously restricted when he was younger. Haesoo and Joowon's relationship started on a whim and dove into something more causing their family to break apart. I personally believe the relationship as a whole is very unhealthy, it's push and pull, built on jealousy, their parents are in love, etc. Taekyung doesn't have that type of relationship with Haesoo, though he has his own issues like going back to Japan (possibly). It's just at least in my opinion as a reader, he will be good for Haesoo. In the recent chapter Joowon asked why Haesoo was getting mad on the account of Taekyung and it was the first time it happened implying that Taekyung does have some sort of space in Haesoo's heart. Taekyung being there helps break up Joowon and Haesoo, and it may give Joowon the time to be alone and actually collect his thoughts. I could delve into how I believe that Joowon is harmful to Haesoo, but know that I do like his character. sorry if i talked too much but yea <3
If I remember correctly, Taku didn't even think about sleeping with Haesoo until our complicated MC suggested so. He was intrigued by Haesoo because of his relationship with Joowon, his brother, as he suspected in the article.
I don't see what make ppl so sure that Taekyung is great for Heasoo? That manhwa is not a nice love story for every characters. Joowon and Taekyung both wants to have their way with Heasoo. And as far the story goes it's all about sex, Taekyung doesn't have something romantic with Heasoo yet. They just have sex only and Taekyung since the beginning want to have Heasoo as an model for his art and sleep with him. Maybe he is not gonna care about Heasoo after he got what he wants from him.
Joowon shares history with Heasoo, they grew up as family and end up in a twisted relationship that they belong to eachother without been the case actually because there was no words about love or be a couple. And now Joowon is frustrated that Heasoo being eventually serious with Taekyung while he was there for him since a long time compare to Taekyung. He doesn't expect that someone in Heasoo life be more important than him because Heasoo doesn't care about anyone but him in Joowon point of view.
Because Heasoo is kinda following Joowon and Takyung flows since he is not very clear with what he wants. He has not say anywhere that he wants a boyfriend or a sexfriends or nothing. He just goes with the flow. I don't think that he sees him as someone that important for Joowon and Taekyung too. That how the author portrayed Heasoo so far.
The story is not that clear about every characters intentions yet.