baby daddy drama

So yesterday after my 12 week appointment my baby daddy that I have been fighting with the past two days had asked me to lunch he had been kissing me and telling me he loved me the whole appointment well we are in the car and I'm picking music on his phone when a girls name pops up and she says " I miss you" I instantly look at him and say who is this and why do they miss you he then goes on to tell me it's a girl he's been talking to for a few weeks because we've been on a rocky road so I throw his phone at him and just get up and go into the restaurant he tells me they didn't do anything but did hang out the other night. Well we get back in the car after lunch because he wanted to talk about everything and I finally got it out of him that he did in fact sleep with her just a few nights ago as she's blowing up his phone the whole time we are talking in the car I'm so heart broken and don't know what to do he keeps telling me we weren't together at the time but I'm almost positive we were need advice on what exactly to do now