It is hard on your own but it will give you and your DD a really close relationship. My DD and I had a few years on our own and I think she secretly would like it to still be that way sometimes LOL
I hope your X comes around and realises that this little girl is as important to him as his DS but its hard for guys sometimes to visualise an unborn baby when they already have a bond with their child.
Good luck in the next few months, BB is a great place to find support so stay in here!