I personally think we split because a relationships not right and if you go back it can never be the same.
This brings problems of each own i.e what each other has been up to during the split.
I'm not sure how old you are but looking at the memories you have of being with your ex when you were pregnant is never going to let you move on.
As said before you have not being fair to your current partner when you're allowing your past cloud your present!! nor are you being fair to your child letting him/her get close to someone which really for their sake you should be honest with.
I totally agree with Karen you need to spend time on your own, be honest to yourself and your current partner.
Good Luck.