Seems like sometimes they go away for a while sometimes they don't but I don't fantasize about same sex when I get off.

My guess is you aren't getting off enough.

Seriously, I would think if you are truly Bi or even gay your feelings towards guys would not change in the period after you get off, when you are horny all sorts of thoughts may go through your mind. Its in the 15+ minutes after the fact that your head is cleared of that. In the manner as my feelings towards women do not go away after I get off.