My mother got into a similar situation with a family "friend". She agreed to be the cosigner on his car loan. Then he moved off to Kansas or wherever and sent a few payments. My mom was forced to choose whether she wanted HER credit ruined or to just pay his car off. She chose to pay the car off (while documenting how much he still owes her). My brother and I want her to take some kind of legal action, but she refuses. She says she'll just be smarter next time.

However, in your situation, I would be livid. Have you told your boyfriend how upset you are that he is allowing this person to do this? Maybe if you explain, like eskie said, that she's taking money from your relationship and causing you to suffer for no reason he might understand.

Any way you slice it, you need to talk to your boyfriend and get this straightened out. She shouldn't be allowed to do this which it seems like your boyfriend is doing. Allowing her to take advantage. Believe me the bill won't go away. He should be getting some sort of payment from her. Even if it isn't equal to what you have to pay out, she should be paying you back as much as she can each week.

Good luck, I hope things work out for the best.