What drives a woman to sleep with another woman's man?

This is something I've wondered about for a very long time. When I was in college, I had a fling with another girl's boyfriend. I thought she was pretty, so therefore, in my mind, that made me prettier. I also knew that he was taking quite a risk sneaking around with me. That did wonders for my ego because I felt since he was taking such incredible risks to see me, then certainly that must mean I was worth all of the effort and energy he was putting forth in order for us to be together. It was an exciting, unpredictable time being his "secret lover", and I am left with many fond memories of the relationship. But I was 19, dumb, and a little girl compared to where I am today. Which leads me to my current question...

What exactly drives grown, mature, adult women to sleep with, and continue to be with, another woman's man? Is it an ego boost? The thrill of the challenge? An attraction to what appears to be a stable catch? And if one unknowingly gets caught up with a married man, what drives a woman to remain in that situation?

I really need clarity on this, as it continues to be a missing piece of the puzzle for me.

Danine Manette