I would assume that someone that doesn't want to be a part of your life doesn't deserve to be a part of your life. Period. Not complicated. Not messy. He's either in your life or he isn't. He either cares about you or he doesn't. He either cares about his unborn child enough to show it or he doesn't. And it really sounds like he's already made that choice.
If he's just coming and going when he feels like it, and going off with other women with no explanation, I would call that a big old flashing bright red warning sign that something is really wrong here. I would say he views your relationship as one of convienience. You're there at his beck and call when he wants you to be, and he invests nothing in it any other time. Either you're someone's convienience, or you're your own person. Which is it? Decide what you want from the relationship, and if your jigsaw puzzle piece doesn't fit with his without mashing the death out of either one, then time for the DELETE key. Done. Time to move on. It's all I've got, Kadie. You either have enough self respect for yourself, or you don't.
I can tell you, there are some really wonderful people out there that happen to be male. I'm friends with several of them, and I married one. I can't come up with a single good reason to waste a minute of your life on a dumb schmuck that doesn't know how to treat you with the love and respect you deserve.