I am beyond hurt and confused

I'm so hurt and confused. I had a gut feeling my boyfriend was up to something. Sure enough I was right. I went onto his facebook that he supposedly deleted and I seen he was messaging random girls being flirty and giving out his number. I immediately felt sick to my stomach. We've had this problem before and I'm really hurt right now. I'm 37 weeks pregnant and we literally just bought an engagement ring over the weekend that he's suppose to give to me on Christmas in front of my family. I'm so angry, hurt and confused. I thought we were done with this phase and now this happens. I called him when he was at work and confronted him about it and he said he's not doing anything as in physical cheating but that still makes me upset that he's messaging girls when he has a child on the way and I'm giving birth to his child in a few weeks or less. I was crying all day I have a headache from it. I don't know what to do, I told him I'm going to stay at my moms for a few days because I didn't want to see him or hear him say sorry when we've already been though this and I thought he'd stop playing games. I feel like I want to leave him but I'm torn and don't know what to do. I don't want my child to not have a father