I would have a talk with your girlfriend. You may find that she is needing a break. It sounds to me like she is not happy with the current circumstances. If it IS only that she is depressed and going through a really hard time... in two years, I would hope that she has gotten some sort of help to get her through it all.

Tell her you are worried about her, and you realize all she's been through - that you DO love her... but that maybe it's time to back off and let her deal with everything else in her life for awhile.

As for your roommate... I would let some time pass between situations. It looks bad on you to both of them if you dont (IMO). That might turn off the roommate because how you treat other women (as in dump one and pick up another all in 24 hours) is an issue that might be a factor in whether she would consider going out with you.