What do I do! I am on no sleep because of this!

I found out that my friend’s boyfriend had been seeing someone. He broke up with her because he admitted he had a girlfriend and couldn’t go through with it. I am furious!! I don’t know what to do. I didn’t leave work until late cause I was so upset. He is constanly telling me how much he adores her and how lucky he is to have her and he does this!!! I am thinking of confronting him and telling him that I know. I can’t let her know, she will be heartbroken! Seriosly I did not sleep last night.

Sorry guys for ranting but I can’t tell anyone and I needed to get this out