Expectant mom

Hi, I'm five months pregnant and very stressed out. I know being pregnant could cause you to be on an emotional roller coaster, I have 2 other children, but this pregnancy finds me more stressed out than before. I get angry at the slightest things. Sometimes it makes no sense why I'm angry but to me it makes total sense. My significant other is going through a divorce and trying to gain custody of his child. I am not prepared to raise a forth child. I don't know if it is jealousy that has me acting this way, but, I don't feel any closeness to this child. This is an unexpected pregnancy also, we've been together for a year and a half and towards the end of last year he left me for his ex-wife for two weeks because she told him that was the only way he'd see his child. He's begged to come back, via e-mail, phone, and so on..I still loved him so I did. He's been trying his hardest to make things up to me. I will admit to that. Very hard. Catering to me, making sure my needs are being met, emotionally and otherwise. But now things are so complicated I sometimes regret taking him back. When we argue, I want to fight, literally. Sometimes I honestly look at him and just hate him for taking advantage of my trust. I've never ever put up with anyone else like this, never gave someone a chance if betrayed. But I did with him. I know this anger could cause complications for my pregnancy, I want to find a way to diffuse it and not think so much of the betrayal and move on. How do I do that?