Why not start out as friends and see how the relationship progresses from there? You don't want to jump back into this, no matter how right it might seem right now. You've been hurt once, so you should naturally want to avoid that as much as you possibly can. Don't let yourself keep falling into this never ending circle of breaking up, getting back together, and break up again. He has a kid on the way, and he's very much about to be a full fledged adult. Is this really something you want to get yourself wrapped up in? Is he really worth the time and effort of it all? Only you can know those types of things, and only you can accurately weigh them. You know what's smart, and you know what isn't.
Are you following your heart, of your brain? Sometimes we can follow either one, and end up in the wrong place, and somewhere we don't want to be. I feel like no matter what I tell you, you're going to decide for yourself where you want to end up, am I right? I could tell you it's terrible, but you know already which way you are leaning.
I just hope that you are smart enough to not let yourself rush into it. Take it one step at a time, see if you see the red flags you seen before, see if he's different, see if he has matured - and above all, see if he's worth the trouble of all of it again. Don't let yourself be made a fool of, but don't let yourself miss out of something that could be great.