Trust Issues - Too Much Pressure

My girlfriend has trust issues and feels as though she has been betrayed by everyone in her life except me. In fact, she loves me more than anything, so much so that if we were to ever break up she said she would drop out of college. She says I am her only reason for being. This puts a lot of pressure on me. She has very few friends whereas I have many, this leaves me spending all of my time on her. I have tried to encourage her to join groups on campus but she is apathetic.

She is now in a fight with her one and only friend besides me. If she loses this friend, I will be the only one left for her to spend time with. The reason they are fighting is because my fraternity chooses "chapter sweethearts" and her friend was chosen above herself. She sees this as a betrayal by all the brothers who voted over it and by her friend for accepting the position. My girlfriend introduced this girl to the fraternity, and many brothers told her that she would be the "sweetheart." This is nothing but a title and a picture on a wall, but my girlfriend has inflated it to ridiculous importance and is destroying the friendship over it.

I have tried to support my girlfriend, while also trying to rekindle her friendship, but she refuses to forgive her friend. Complicating the matter is the fact that they are roommates and this girl is a girlfriend of one of the guys in the fraternity. They will not be able to avoid encountering each other. I cannot break up with my girlfriend not only because she might lose her mind, but also because she is the most vindictive person I know. She will hold a grudge against me for eternity, and on such a small campus, I would have to deal with her at the very least weekly. I love her but I see no options. How can I get her to forgive her friend? What can I do to relieve this pressure?