Being cheated on

So I recently found out I am getting cheated on by my "boyfriend". I found out from his roommate which I trust and the girl he slept with. The girt is really sweet and didn't know me and him were dating. I talk to the girl and were coming up with a plan on how we should confront him about it. I still love him but this is a lot for anyone to handle especially knowing now that he's done it in all his relationships.

PLEASE HELP