Wife’s Past

I find it weird that I am turned on by my wife’s past lovers. I didn’t always feel this way. I had the normal jealous husband attitude. The thought of her with someone else was hurtful and made me angry. I knew she had sex with some boyfriends before we were married but that is all in the past. Never really thought much about that.
I started noticing a little strange behavior about eight years into our marriage, noticed it for about two weeks. I just up and asked her one day what was going on. I asked her how jokingly, are you seeing someone else on the side? She confessed to me then that she was having an affair with a guy she worked with.
As I listen to her confess I grew angry of course and hurt but also had an almost immediate erection and inside found it to be a strange turn on. To condense the story, she stopped seeing the guy but two years later had another affair that lasted a little longer and then that one ended. But strangely after that itall played on my mind and I wanted to know more and every detail about the guys she was with. Every sex detail as I was turned on hearing about other men making love to my wife. Why is that a turn on?
Ther must be some psychology to this.
She has not seen anyone else in many years.