Quoting Jax in the Tardis:" http://mobile.cafemom.com/group/115189/forums/read/18156586/\
I would wonder what made him desire to make her happy, but what's done is done.
Pretty much what she's doing. I would be furious but there's nothing you can do... Personally, I would be so angry and hurt I would need time to my self to cool off... and from then I would do everything I could to make sure they were informing themselves about parenting decisions, work, their future, how they planned on getting the hell out of my home (although I would probably prefer they stay until they were able to absolutely afford a safe place within reason), and maybe talk to the girl about counseling to make sure this isn't a recurring theme in her/their life... I don't know how I'd feel about the marriage. I would be proud of my son for telling her dad... that takes some balls lol.
I don't know if I'd expect him to work full time as much as her work through pregnancy part time, too, so they can have room in their lives for college or training after high school. I would let her move in because I wouldn't want my grandchild on the streets (I'm assuming that an abortion is totally out the question for the GF).