Sticky situation with my first love and his new girlfriend...?

Its the summer time and im so happy that me and my 1st luve are actually communicating..but the problem is he still is with his new girlfriend..the thing is that when is around me i ask him questions about her and he always will return it with "i don;t love her", "she is full of drama all the time", "i miss being with you", or just some off the wall story why they aren't talking at the moment...So one night i invited him over and we become intimate i know that he isn't drunk and he knows what he is doing so he is definitely cheating on her...the very next day we text about last night and everything then i go on facebook and his status says "i love you" but it wasn't to me it was to his new girlfriend..first off im shocked that he even puts that on there and i also feel sick to my stomach that i allowed myself to fall for my first love like that and also for him to cheat and act as if nothing happened..my question is should i tell her what all went down or just have a conversation with him about the whole thing? any advice or comment you have i will accept ;)