I don't think you can ask another to change their life (I guess you can ask but can't "demand") in that way, especially if it's about a problem in the past. If your girlfriend is having an affair now, it doesn't sound like she wants to be in a relationship with you (or actually, it sounds like you shouldn't be in one with her). Everyone has to stand on their own two feet and make their own decisions/mistakes about themselves and just limiting another as with having your girlfriend quit her job won't "protect" either of you from such situations.