How about being a man, and gently telling her that you don't love her. That seems preferable to making her life hell, so SHE will break it off with you! Quicker, too. (She likely deserves a better man than you, anyway!)
Show up to her house with another man telling her "honey...we need to talk" and then proceed to smile and look at said male.
Demand she suck your dick. Every 15 minutes. Around the clock. Then cry for 30 minutes after every time she does it. She'll get tired of you pretty quickly.