Hi, sorry about your situation you sound like a really nice bloke who wants to do the right thing which is not always the way now-a-days.
Firstly, you dont need to be in a relationship to be a good parent to your child. You just need to be in the childs life always not just when it's convient to you. Which means if you get into another relationship your child still knows that he/she is loved just as much.
Secondly, as soon as the baby is born get a dna test done make sure the the child is yours from the get go. If you dont get a test then if ever you and your ex get into an arguement she will tell you the child isnt yours just to hurt you. I've got friends who have done this!!!! Also you'll know where you stand if you dont know for sure you may not love the child as much as you should because the doubt will always be there.
Just because your ex says the baby is yours don't mean it is.
Also are you positive that she is actually pregnant and not just saying she is because she knows this is something you want?? She won't be the first person in the world to lie about a pregnancy to get her man back!!!
If I was you I would buy a home pregnancy test take it to her and make her take the test whilst your there so you can see for yourself.
Good luck I hope things work out for you.