Something in your bfs gut told him this was wrong, but it made his cock harder and his hole looser so he ignored it anyway. He felt your best friends cock slide inside him raw, in a car parked somewhere sketchy since they had nowhere else to go cheat
It doesn't matter that he loves you.
It doesn't matter that he enjoys you.
It doesn't matter that he said he wants to be with you forever.
He'll still choose to cheat for his real type.