If that’s the case there’s only two real options if you want to feel better in the long run. Confess to him and see if he’ll destroy his current relationship to be with you.
I’m not going to lie, that doesn’t really make it more complicated. He still chose someone else the second they were available instead of you whether they are toxic or not. Also he’s currently with a man? More power to him but are you sure he is bi?
Well if you think he has feelings for you just tell him and see what happens. But if he doesn’t want to leave his bf after you tell him you should probably cut your ties with him. It’d be better for you in the long run.