Don't feel bad for wanting to get married, will you? When I met my DH he was very much the unconventional type - had lived on boats, was an artist, etc etc - and I felt like a total middle-class square for wantring to get married & do it properly instead of shacking up on some houseboat, spitting out billions of kids and being barefoot all the time.
I almost let this change my mind, but I had my Mum's voice in my head so I couldn't! Now I feel proud of myself for sticking to my guns, as if we split I'd be so much better protected. My neighbour had a child with her live-in BF who vowed never to leave her, then he left her & she had to sell the house to pay back his share and she has no legal rights at all.
What are you going to do now? In a way, you might have to give up the romantic ideal of his begging you to marry him because he'll just die if he doesn't, and just be a bit boringly practical about the whole thing.
So many men hate marriage that I don't think it's a Bad Sign if he's unenthusiastic, especially since you already live together and have a baby on the way so he doesn't need to get married to have you around 24/7. But, because you have a baby on the way I think you should go ahead with the marriage idea, just to ensure you're protecting yourself legally.
If you're like me, you'll hate this because it's not the lovely romantic dream you always had, culled from films & books, etc. But it's still worth it.
If you don't want to "push" him into it, you could steel yourself to tell him, calmly, that you don't feel comfortable staying with him without the security of marriage, so if he can't or won't marry you, you can't stay in the relationship. Not in an ultimatum "It's marriage or nothing!" way. But in a, "I know you don't like the idea, but I need it to feel safe, so I can't carry on without it. It'll break my heart but I'll have to finish our relationship if we don't get married, because I simply won't ever feel truly secure without it." Then leave it for him to decide. It's fair enough, really, isn't it?
He sounds like he IS very committed already, to be honest, so it shouldn't be that big a jump for him to make. (Which is why he's already agreed - so many men wouldn't have done that.)
I hope this isn't lecture-y or anything. I feel for you, and I know exactly why you want him to want to marry you. I was just the same. It is important, so don't feel you have to compromise what you want in order to stay with him. You'd be better off married than unmarried, that's just the way it is. So fight for your rights!