Really needing some advice.. Please help.

I really hope this isn't marked as spam, but I'm in this situation I desperately need to write about because I'm lost and I don't know what to do.

I'm engaged.. Well I was engaged. I'm the one who broke off the engagement. And I'm about to tell you why.

My fiance, Ryan, has been talking to this girl. Like.. talking talking. Talking talking as in.. talking about dumping me to go be with her and how he's tired of me and tired of my shit alot.

I asked him not to talk to her anymore because he can't control himself just being friends. My brother is good friends with this girl and I guess he always harasses her.

He promised me he wouldn't talk to her at all anymore, because he assured me that he wanted to be with me and be mine, and yadda, yadda, yadda.

Recently, I had this feeling he was lying to me about it, so when he was in the shower I went through his phone. He had some girl saved as Erica in his phone. I got the number and come to find out, it was this girl all along.

He lied to me for almost over two months and still tells me he loves me, but, I don't trust him at all. If this happened to anyone of you, what would you do?