For me it's the top because he used to be fooling around with the others but he's looking for uke soo i think it's kinda red?
So what if he fooled around? Is he not allowed to have a sex life? Was he supposed to wait around for his one true love forever? That doesn't make him a red flag. Kei is a red flag for accusing Taiga of lying about his feelings, pushing him away, and when Taiga was planning to leave and set him free, that's when he decides that he wants to be with him. No apology, nothing. Why did Taiga have to be the one to carry the weight of their broken relationship? Kei didn't even bother to put in any work.
Just saw a comment saying the bottom is red flag, real. If you put this in Taiga's (top) perspective you can see how Kei (bottom) handles relationship or hook up.
The bottom didn't even say sorry for judging the top and branding him as a liar. That's why this feels short.
Anyways, overall, the story and art was so good.