I feel for you OP. Very tough decision. All I can say is that
if you commit to your GF and new baby you will find a way to make it work. When we decided to have our second child the timing was awkward; I was a (very) mature student and the baby was due right on finals, and obviously I didn't have a "proper" job either. Baby was slightly premature, got through finals (excellent grades), straight into a new job, all with hardly any sleep

It was awesome though, to be honest. We were both 100% committed to making it work, and it was a amazing motivation for me as well. Looking back I can't believe we made it through, but it's something I'm proud of beyond words.
Obviously your situation is very different, but the point is that
IF you can make this all work, it will be something immensely life-defining. You will come out of it a much stronger and wiser person, and I can pretty much guarantee you will love the little guy/girl unconditionally. Of course there are no guarantees with your relationship, but hey, there are no guarantees for anything.
Good luck with whatever you decide. I certainly wouldn't judge you if you felt this wasn't the right time.