What's your problem? All I see from what you wrote are complaints. She is paying what she has decided to pay and you are paying the rest. If you didn't like that arrangement, then why did you rent with her? If she has violated your agreement and has invited in a boyfriend and has given him a key, then you have choices. Tell him to get out and tell her to tell him to get out. If she won't, then you are stuck with a sh*t roommate who has no respect for you - that's who you chose to rent with. What do you expect us - YA to tell you when you chose her to be your roommate? When your lease is up, move. That's all you can do. Well, you can try and make it miserable for them but, that works both ways. Annoy the heck out of the guy. Make your roommate's toothbrush disappear. Nothing expensive or non-replaceable, just very annoying. Then, two weeks later, it disappears again. But, that might get tiresome.
Certified Paralegal, with 25+ years' experience & with Landlord & Tenant law experience.