Decision Time: Mom or not?

So ive been with my girlfriend a long time, but her mom has always been against it and weird about it. The latest news is i visited my girlfiend at her house when no one was there and the mom got there. We werent doing anything wrong but i kinda sneaked out because i wasnt sure how the mom would react. She found out and now shes really pissed and has given her daughter two simple options. 1) Get with me(as in married now, we`re only 18 years old) or 2) Dont stay with me and not see me behind her back, and in return her mom will pay her College, which she starts in a couple months and of course other needs my girlfriend might have. Basically, she will remain dependent on her mom...I made the decision with her(my gf) that i will wait for her. Give her the time she needs to fix things at home and start, at least, getting independent with things and all of that. Did i do the right thing? is there anything else to do? I know the waiting will be hard, and i think im scared...sooo. Now what?