Anyhoo, Intrasearching, I think it's wonderful that you've gotten to know a kindred spirit (your girlfriend).
However, the both of you have a lot going on . . . personally within yourselves, your college studies, she and the ex boyfriend/now roommate situation, you've mentioned your parents a couple of times (so I kind of think something is up with them, eh?), and, man oh man, when you're young you've got all those wonderful hormones wrecking havoc too!
It sounds to me like your girlfriend is stuck - stuck either thinking she has no other option of finding another place to live or afraid to leave what's familiar / comfortable. I liked the suggestion that rather than focusing on your concerns that she may leave you, that if you focus on her long range health that it will also help yours. At the very least, living in a different situation for her will help her to develop her own self, so that when she's really ready to settle down with someone (hopefully, you) she'll do it from a place of wanting to rather than a place of need.
That goes the same for you also Intrasearching. My guess is that the relationship with this girl either is one of the few, if any, really close relationships you've had with a female. Nothing wrong with "saving yourself" - but a whole lot of stuff goes into forming a long, long term relationship. Forming a relationship based on need or similarities in backgrounds isn't always the most healthy in the long run.
You don't want to lose her. But the reality is that you could at any moment and for a variety of reasons. So all you can do is focus on your own healing, acceptance of yourself, do what you need to do for your own well being, now and in the future, while giving her the support she needs to heal from the past as well. You do that, and regardless of what happens between the two of you you will know in your heart you did your best for yourself and for her.
Does this make sense?