Your anger is misdirected. Please, please, don't out the guy. The repercussions sound awful and I know you are hurting but this is not the way.

Your BF is a cheater. He's for the bin.

Just a point on this part...

'He also told my boyfriend he cross dressed with girl’s lingerie and even wore his brothers girlfriends clothes before. He’s so messed up.'

I don't know if I have read this wrong but it sounds trans-phobic.