
1. The stepbrother thing doesn't bother me.
2. The toxic thing:
I admit that they are kind of toxic. They are hurt and like to hurt each other and it's pretty cruel to watch. But the cause behind it is their love which they can't openly show for each other because of their parents and Jowoon's job. They love each other, but can't be together because of society and family and that hurts, so they hurt each other (which is not okay). Additionally, the whole first love experience in school was really a bad start for the relationship. They were so young. They shouldn't have had to deal with such issues. If the school or the parents would have known... And that's were the hurting starts. And continues.
But it's not because their personalities clash or something else. Their toxitity comes from the OUTSIDE, not the INSIDE.
And that's why I believe that if they were sure of each others feelings and really started a relationship it would work out. And the understanding of their parents would immensely help. At this point a relationship between stepbrothers isn't a big deal anymore. The family is already destroyed. Them allowing it would just make it better.
3. Honestly, there are WAY WORSE toxic relationships in Yaoi World. Especially, sex without proper consent, etc. Which doesn't make this okay gut I definitely see hope for them.
The author will probably choose Taekyung. Maybe to not be critized for forcing their character into a toxic relationship. And in any other book I would welcome it but here... My heart hurts was too much when I look at Jowoons and Haesoos tragic relationship and I just want them to clear up all the missunderstandigs and stop hurting and get together like they always wished.
But if the author chooses the realistic way, that won't happen.

This is the best ML of all! So cute and precious!! (≧∀≦)
With the other ones I am usually like:
"Well, fine. I guess I have to deal with this kinda urgh ML now. (〜 ̄△ ̄)〜"
But him... I wish I could just steal him from the book! ε=ε=(ノ≧∇≦)ノ
No non-consented things, he isn't cold and acts arrogant and sleeps with woman (like the usual ML) or behaves like an 'alpha' (BARF! EW!) or just prohibits her from doing stuff and his jealousy is soooo cute and totally normal (could even be more).
Oh my god, I love this!!!! The twist warmed my heart. I love this so much!!(≧∀≦) Wish there was more. There SHOULD BE more! More mangas like this!