I am exasperated and this site is the last place I can think of to ask for help.

Here is my situation:
This is a roommate problem. I moved in with my roommate January of 2009 into a two bedroom apartment. We were friends before we moved in and we both attend graduate school now. Things were fine in the beginning, but have slowly degenerated into a high stress situation. The problem came in March of 2009 when she started dating her current boyfriend. Things were fine in the beginning, but after a while he started staying at our apartment more and more. Now he is basically living there for free, despite my protests. When I say basically living there, I mean he sleeps over every night, has food and beer in our fridge, does his cooking for the week there, he uses our machines to do his laundry, he is at our apartment when she isn't, and he has a key to our apartment so that he can come and go as he pleases. He is there when I wake up in the morning and he is there when I come home at night. My roommate thinks all of this is perfectly fine. I have had serious conversations with her about this problem twice now. I told her that I am tired of paying half of the rent on an apartment so that he can live there for free and I can feel uncomfortable all the time. All she can tell me is that they are comfortable the way they are and they are at the point in their relationship where they would like to live together. That would be OK, except I still live there. The only difference from before and after me talking to her about this is that now he is in her room sometimes instead of hanging out in the front room. I am at the point where I don't think talking to her about the problem is going to solve anything, but I am not sure what action I could take to get through to her. There are clauses in the lease about not having prolonged guests, and about not letting anyone besides the tenants have keys to the apartment. Is this something I can talk to my landlords about? I would just move out, but we are stuck in a lease until this December, and I don't think I can afford the $2000+ fee for breaking a lease. Is this a lease issue? I can't put up with this the rest of the year because it is affecting my ability to do school work. I guess what I am asking is how can I convey to her that I am not going to put up with this situation any longer, and that she is the one being unfair?

Yes, report this to the landlord - but be prepared for your roommate to develop a very bad attitude toward you.

OR hand a bill for his third to her boyfriend (IN WRITING) and be prepared to take him to Small Claims Court if/when he does not pay.

Either way you will have difficulties with your roommate - but how much of this behavior can you put up with?