You can love someone and not want to make a future with them. You started with him very young. Your perspective has matured. Obviously you have great capacity to love, so there is likely to be another one in your future - one you do want a future with, or stay with this one and see what happens. Things can change.
run don't walk
Listen to your gut here. You love this man but don't want a future with him. Be strong and stop stringing him along. Tell him that you've both grown up and changed and that you don't want the same things anymore. It's so easy to stay in a relationship out of habit or nostalgia, but then you are always living in the past. Leaving may be the hardest thing you'll ever have to do, but nothing worth doing is easy. I wish you the best of luck in finding the perfect person for you.
I don't know what I'd do, if you really love him, make your choice, if you can't get over the fact he had a baby with another woman, let him go. I think either way maybe you should tell him this so he's not in the dark
I hope he's paying child support cause if he don't you will if you're together
Cut your losses
Is the baby mama drama the only reason you don't want to marry him?
Then you can get around that. You don't have to deal with her at all.