It really depends what the fight was about.? But if it's an on-going major issue then I would ask her if this is really the kind of life she wants for herself and her baby?
I see it like this:
The guy don't want to take responsibilty and act as an adult. He still want to be youing and wild.
A part of me understands him, really. I hate when my gf goes nagging if I have a night out with the boys, but it's wrong if you got a small kid and if it's every week.