What do I do...

My s/o and I have been together for a year and a half and 3 weeks ago found out we're gonna have a baby and this past month just signed a lease for a year renting a house together that we just moved into this past week. I don't know what made me do it but earlier today I went through his messages and seen he's been texting a girl he used to hook up with. Mostly small talk except on 1 occasion he comments that her boobs are amazing and on another they're talking about how he's never made another girl cum as much as she did. Also, browsed through his photo album and there were videos and a photo dated a little over a year ago after I personally helped him move into his new place (before I started staying with him) well there was a video of him having sex with another girl. I don't know what to do. He's always said he never cheated on me and when I confronted him he said we weren't together at that time but yes, we were. We just weren't 100% official. And asking why he's talking to the girl about her tits and how she cums his response was "what, she has nice tits" all day he's just been downstairs watching movies while I'm upstairs with a broken heart and hasn't tried talking to me about it, nor apologizing. I just really don't know what to do and I'm thinking about getting an abortion. Please help with some advice. Do these things happen in relationships? Should I be pissed finding out he cheated over a year ago? What do I do about the girl he's talking memories with? I need advice asap.