When the trust is gone it's time to move on. It's easier said than done but it's true. He needs to build that trust and prove to you that he's serious about you and your child. Don't let him off easy, that just makes it okay for him to disrespect you again.
If you don't trust him and don't see it working out, then let him go. You need to focus on you and baby right now. It will be hard being a single mother. You just have to ask yourself "will I be happy with this decision?" Don't let others decide for you.
I wouldn't either. Plus since she's his baby mama then she's going to be in his life for quite awhile you're always going to wonder if anything is going on again and that's never good. You should always be able to trust the one you're with