That sounds like a serious question, and those are crappy answers!. If you feel she is using you, sweetheart, you need to talk to her about it. Be honest with her. Tell her how you feel. That is VERY important. You are too young to have your life ruined by a jealous woman.
Tell her you can't be anyone's sex slave. You have to be free to leave if you want to. If she continues to put you under emotional pressure -- emotional blackmail -- then back off and don't see her for a week, or two weeks. Don't answer her calls for a few days. Give yourself some free space to think things through and decide how you feel about it.
Go with your gut instinct. Don't be pressurized. Don't listen to her if she threatens to harm herself. You are not responsible for someone else's foolish actions. She is responsible for herself. You are responsible for yourself.
In the meantime look for a lover who is not married. Good luck to you!