from experience of being depressed as a teen I found that even now as an adult sometimes I fall back into those days where I can just wake up and be in a negative environment that can get me down sometimes. To come out of that I have to just get way from it and find or go back to a place or thought that I can be relieved from the stress. I find that I get that way when I am in groups or alone. As far as my relationships with guys I've dated I feel a since of peace and positivity in myself that I feel when I am one on one with a person verses a group of people. I don't know your girlfriends circumstance but you really do need to focus on her and communicate those feelings with her and help her get to that happy place.