Whoa, this is really one tangled web that was woven (try saying that five times fast, lol).
Anyway, I wouldn't blame you for not being okay with being friends with him if he became a dead beat dad. I admire you for being his friend and advising him the best way you can, I think you are correct in telling him to get things straightened out long before the baby comes. She does so a bit . . looney, so I hope he knows that a whole lot of crazy is going to be coming his way in regards to her and his child.
Does he know for sure it's his?