Feeling hopeless

The past few days my fiance and I have been arguing. I feel like no matter what I'm never good enough for him. Sometimes he gets in these moods where he loves me wants me and then other times, when he feels like everyone hates him, he pushes me away and makes me feel like garbage... I've been with him for a while and we have a son on the way. Recently I've been thinking of leaving him because I honestly cant handle it anymore... every day i dont know what is gonna happen. I dont really have anyone who may be willing to take me that I know of and I dont want to be a burden to anyone with my son who will be here in a 2 months. I just want a better life for me and my son. I dont want to have to wake up every day wondering if it's going to be an argument or a good day... have any of you ladies gotten out of situations like this?

Update: we tried having a conversation but he went right back to how he was. We talked about him seeing a doctor or something and he say yeah we should, but then he makes excuses or says he doesn't want to. I dont want to be around someone who has the opportunity to help himself. I cant keep supporting someone who doesn't even want to try. I need to have a better life for my son. I dont know how I am going to go about leaving but happening...