Feeling Betrayed

Here's where it gets sticky:

He's been acting kind of off lately, which has made me suspicious.  He got me absolutely nothing for our first anniversary, not even a card (I got him a cute card).  I thought he would at least get me a card, maybe some roses, so I was really let down when I got nothing.  When I gave him my card, his response was (jokingly?) "ugh you suck, I didn't know we were doing that!"  Weird, okay. 

Tonight he went to bed early and left his phone out in the living room.  Curiosity got the best of me and, well, it turns out he has been sexting a former student of his.  He said things like "I've been thinking about trying to make you ***", "I need a hot makeout session with you- I need to taste those lips", "our plans keep getting ruined somehow". 

I am floored.  Years ago early in our relationship I caught him texting another girl and I packed up all my shit and said we were done.  He sobbed and sobbed, said it was a huge mistake, didn't know what he was thinking, etc.  I told him if it ever happened again then that was it.  That was before we were even engaged.  Now we are MARRIED. We said vows in front of all of our family and friends (some of his friends flew from CA to RI for our wedding!!) and I can't believe he would betray me like this, especially after all we've been through.  We finally have our rainbow baby and he has stomped on my heart. 

I haven't talked to him yet because he's sleeping, but I don't think I can trust him anymore. He had a shot and he blew it. Not to mention attempting to cheat on his pregnant wife!  Now what, though?  Am I horrible if I do decide to get an abortion?  I'm so distraught, but the thought of being a single mom and having to deal with him forever after this is just killing me.  Our plan was for me to take grad school classes after baby was like a year old.  Please no religious comments about abortion... I do not want lectures or harsh comments please I already feel so broken.