My wife and I were good friends in high school - my best friend had a huge crush on her. She and I nearly hooked up fall semester of our senior year, but things went a little awry and we went back to being best friends (or so I thought).

Around Christmas, we had a phone conversation about whether I should go on a date with this semi hot (but very popular) chick who basically dropped some blatant hints to a friend of mine that she wanted to go out with me.

A week later, my future wife called me up and invited me over to a girls-only New Years Eve party she and some friends were having. I was making out with one of the other girls. When my makeout partner went to get another drink, my future wife seized the opportunity to sit in my lap and make it clear that she wanted me. Other girl comes back, gets pissed, hilarity ensues. I end up in bed with both of them later that night. Those were the days.

I'd go with the jealousy thing.