ually frustrated and afraid of what I might do?

I'm 21(almost 22), and my girlfriend of 4 months is 19. She does not get along with her father and he obviously feels likewise but I dont believe there was every any abuse of any kind. This seems to stress her out, along with the fact that she has two jobs and we usually see each other really late at night. I love her and she loves me but it seems as though all I ever do when I see her is pick her back up and just barely get her out bad moods. I dont mind doing this usually because of course I like making her happy. I love everything about her and know she doesnt cheat as she's kind of traditional and we spend all our free time together but the low drive she has, just seems to get worse and I end up feeling sort of depressed over it. A couple times she has said she is aware of my need not being met but says she is simply sorry. I am really starting to feel depressed and it affects other parts of my life. Neither one of us likes the fact that I use o to get off either.