Oh! my! Déjà vu !
One of my friend and her EX went through the same thing...
They started dating in High school and 8 years later, they asked themselved what it would be like to have sex with someone else (they were both 1st lovers went they started dating...). They both agreed that they just want to see how it is with someone else I was totally against it and told her that a penis is just a penis ; what counts the most is that you love the person. Well, she went on with THE PLAN: for 2 weekends, they would be aloud to go out and have sex.
She is very pretty so she didn't have a hard time to get a guy to sleep with her but... on both occassions, she couldn't go through with it, she wasn't comfortable with the other men... well I wasn't going to tell her : I told you so!" since she told me herself and couldn't wait to see what her boyfriend did on those 2 weekends. Well... as predictable as this my seem, he got the chance to meet a girl, he saw her on those 2 weekends but never had sex with her because he started to like her and din't want to have sex with her just because his girlfriend said he could ! How pothetic!
After a few weeks, the relationship was "rocky" since all he was thinking about was the other girl... it came to an end 2 months after and today, she is sorry for asking her ex if it would be ok to see other people. As for him, he is still with the other girl, and from what I've her, things are going great.