A little background: My wife and I met in high school. We've been together now almost 16 years, married for 9. We lost our virginity to each other, And had been each others one and only for the longest time.
Around 2008 I saw her browser history. It was full of women being fucked by two or more men. Not wanting secrets I brought this up to her and asked it if was something she wanted. She said it was a fantasy and we left it at dirty talk during sex a few times. Then it became every time we had sex, the idea of fucking someone else came up. I eventually opened up to the idea and it almost became a fetish for me, to share her. It finally happened one night (memorial day weekend 2010) with a very good friend (who I am still friends with). After a night of drinking one thing lead to another and a MFM was had. Lots of fun. This went on for a few years, with me never considering having sex with someone else.