I cheated on mine, felt horrible about it, and know I wouldn't do it again ever. I don't think to myself "I don't love her because I cheated on her," I'm just weak.
You're not weak! Don't put yourself down becuase you made one mistake. I know I made a mistake and ended up cutting myself but then I realized I had somethings that were going for me....Like my art, my friends and my current b/f. I have cheated before and I felt like you did. Horrible. I wasn't sure what to do until they both found out and left me.