I want to have sex with my brother.

I will start by saying he is not actually related to me at all. We were adopted as teens by the same family. We have slept together before, but it never led to anything and then I started dating my fiance. I know that I shouldn't want to do anything with anyone else, and I have no interest in other men. I completely cut contact with my brother after I started dating my fiance, and he was still hitting on me after I told him to stop. But for some reason, I keep thinking about when we had sex, and I want to find him and do it just one more time. I won't, but I don't know how to get this feeling to go away! I don't even actually like men besides my fiance. My brother and I just got really close. Help me? EDIT: It has been two years since I have even seen him. And I did say that I am not going to cheat on my fiance. I just want to get the thoughts to go away.