I am 20 years old and engaged to the girl of my dreams. "Liza" is beautiful, smart and very loving. We have no problems in our relationship.

Before she dated me, Liza dated one of my best friends. In fact, I once witnessed them making out at a party. The problem is, every time we become intimate, that image plays in my head. I know what happened before we dated is not really my business, but I feel I should let her know what is bothering me.

I know Liza would never cheat on me, but how do I tell her something she did in her past is affecting me every time we make love? － Troubled in TexasDear Texas:

This isn't really Liza's problem－it's yours. She cannot do anything about the images in your head. It's up to you to replace those troublesome pictures with something else. Whenever you start to remember Liza kissing your friend, make a conscious decision to envision something more pleasing－perhaps substitute your face for his.

If you do this each time, it will get easier and, unless you deliberately bring up the old images, they will fade away. If you cannot do this, you may be on your way to a total obsession with thoughts that will eventually destroy your relationship.