Sadly, while he is obviously an immature arse, to say the least, you don't have a choice. You got pregnant by him, you're stuck with him, so is your baby. You have two options. 1, to have a civil relationship with him and his partner and involve him in your baby's life, from birth through to making polite conversation at christmas concerts, graduations, your grandchildren's birthdays etc for the rest of your life, hopefully collecting some support, maintenance, and parenting involvement along the way (which you will need and your baby will benefit from) or 2, you can cut contact and chance it that at any point in the next 18 years he won't go to court for parental responsibility, get an order for shared parenting and tell your child what a wicked mother you are to have cut him out of her life.
However angry you are, I'm afraid this is the reality, unless you have evidence that he is a risk to your child. You also don't know yet whether his 'soulmate' is going to turn out to be a one month wonder or the world's best stepmother.
Detach, try to relax, plan your life on the basis that his involvement is a minor detail if it happens, not a big deal. Don't encourage him, don't make it easy for him, but don't give him reason to create a big 'she won't let me see my baby' drama either.
Sorry to be blunt, but that's the long term reality. Big hugs to you, he has obviously really hurt you but you are well rid of him, and better that he has gone now than when your baby is attached to her daddy. Fill her life with people who love and care about her and a crappy unreliable/ absent father won't define her life.