It was more the fact that she was derided, but not me. Does that make me a slag? Possibly, yes. Do I feel any remorse or guilt about it? No.
We have both moved on from the relationships we were in at the time. To this day we remain close friends, in fact I would say in many ways we are each other's closest friend. We still love each other, just can't be in a relationship with each other. That's why the sex thing wasn't, and isn't a big deal for us.
Right on man, the double standards for men and women's sexual behaviour are strange. My personal opinion is that most people these days, male and female, don't take sex as seriously as they should sometimes--but regardless, men can be sluts too, and actually, the number of partners one has had (to a degree, anyway) isn't the only factor involved in that label. If someone's had 8 loving relationships and slept with those 8 people, that's less "slutty" (IMHO) than someone who's only been with 3 people but they were all random hookups. Gender still not being involved in the decision.
Anyway, sorry to go off-topic, was just glad to see someone else with a logical head on their shoulders.
In response to the OP, I wouldn't sleep with an ex unless I was back in a relationship with them, as I can't really get into someone sexually without a corresponding emotional connection. So no, haven't done that.