Not sure what to do HELP!!

So before I found out I was pregnant (I'm 14 weeks) my SO and I enjoyed going out quit often with friends for some drinks. Now I'm obviously not doing that. I don't mind my SO going out once in awhile for a couple drinks with his buddies. Last night however I fell asleep watching a movie on the couch and when I woke up at 1 in the morning he still wasn't home when he got off work at 10:30. I look outside only to find that my car isn't there. When I call him he says that he's at the library (local sports bar). Again I wouldn't mind but the last time he took my car to the bar he left it there when I had to work at 7 in the morning. (I don't want him to drink and drive obviously but if he's going to get intoxicated he should have walked to the bar). Well when he finally does get home it's three in the morning (the bars have been closed for an hour) he has a girl (Rachel) that he knows I don't like but am friendly with (also the town sleep around), with him... Now let me back track a little. A few weeks ago he basically did the same thing but he came home with a girl (Kelsey) that likes my brother (whom we live with) and without my car earlier in the night. So I was pissed because again I had to work at 7 in the morning and I really did not want to get out of my pjs to walk to the bar to get my car at midnight. So he gets all pissed and 'goes to get the car' with Kelsey. Well 3 hours later it's 2AM and they still aren't back. I go outside at one point  (probably close to 4AM) because my dogs are freaking out a little. Well apparently they have been sitting there for hours just talking in our driveway in her car. Yea my car still wasn't there. Needless to say I was livid! We worked things out or I thought we did until last night. 
So last night when basically the same thing happens he doesn't understand why I'm so pissed. And thinks he has don't nothing wrong. 
He also gets extremely mad about the littlest things. The other day he got upset because I started a puzzle without him. Or he gets mad because I don't wear the bracelet he made me enough. Or I don't involve him in the pregnancy like he thinks I should ask him everyday of he wants to see what glow says today instead of asking me. But when I get upset over something instead of understanding or trying to make the situation better he just get all mad too. It's like a never ending cycle. He tells me I'm selfish all the time for not doing little things or including him in little shit that I have never had to include a guy in before. My brother who is his best friend even thinks it's absolutely ridiculous. I just don't know what to do. Do I try to stick it out and make it work? I love him but it's just getting so hard and love shouldn't be hard. Or do I make him move out of my house and have it be my baby and I against he world? It's just so hard. I guess leaving someone is easier said then done. 
Oh also a quick side note; he has a 5 year old son from his previous marriage and truly is but isn't the greatest father to him. That is half because of his ex wife but also half because of him. 
Not sure what to do. I just feel so depressed and so lost when what I really want is to be excited about this pregnancy with someone that wants to be excited about it as well. 
Sorry for the rant, I know it's long but any help would be greatly appreciated!