It sounds like she pretty much blackmailed him into it by threatening to move away. If as said by Diz, that he comes back into your life then whilst it may seem to be a good thing, you will have to change your perception of the relationship you did have as he will be a father and may continually be at the beck and call of his ex-girlfriends emotional whims, in order to maintain contact with the child. You will need to satisfy yourself that this would be ok for you before recommitting to anything.
Again as Diz has also said, you have been through it once. There might become a time when you just have to accept that � rightly or wrongly - he has chosen his child and this woman over you. I know that hurts, but it is the simple fact of the matter. You have coped before and you will again. You are not destined to be alone, and I hope that once you have let the dust settle on this relationship you find another true love. It happens to us all at some point in our lives.