Hi, I'm replying because I just wanted you to know that I have read and I really feel for you. I was in a very similar situation a few years ago now and I sooooo wish the choices I made then were very different, if they were I wouldn't be going through the crap that I am.
I have a very jaded view on this because of what I am going through personally, so my opinions I think will be very different to many on here..... but here goes.
your XP sounds like a twat! If hes the sort of flighty person to not stick around whilst you are pregnant, is he really going to be there once baby is born? Have you thought about the future, what might happen if you meet someone else? what happens if XP meets someone else and obviously decides he wants this person to be part of your childs life. How will it feel if you move on and meet someone who is a good father figure, but you still have XP floating in and out of babies life and causing problems (serious problems, maybe) How will you feel if you don't meet anyone but your XP does and wants that person in the babys life, even if that person is as much of a twat as your XP??
Everything I have just said I will be thrown to the wolves for as most on here are of the view that a child has the right to a relationship with both parents (I'm not) I'm of the view that if a parent is a complete let down, is inconsistant, is a compulsive lier, is manipulative has no moral fibre whatsoever that that sort of a parent is NO GOOD and a child is better of without them.
It is completely up to your if you feel very strongly that your XP should have a relationship with the baby and visa versa in which case you will have to put up with this person being in your life for the rest of your life.
If I was in your position (my old position) I would run to the hills, move as far away from XP as I could and raise the baby by myself, I wish I had done that instead of feeling obligated to giving my baby (DS1) a relationship with his completely useless let down of a father.