Yep, that's my wife, as well.
We started in college. We were living together, and I was realizing she was a nympho and I was mediocre at sex. I discovered that she was cheating on me with a good friend of mine. Luckily for her, that's when I realized I was a cuckold, lol. I didn't want to lose her, but I was incredibly turned on by the thought of her fucking my friend. I played dumb and even tried to make it as easy, as possible, for her to have as much sex with my friend as she wanted.
It eventually all came out in the open. I thought it was over for her and I, but when I told her she was forgiven and that I was aroused by her cheating, she was intrigued. I told my friend about my arousal, and he was intrigued, as well.
We decided to do a threesome. The three of us started playing together, but then I just started watching, them go at it. I quickly realized why she enjoyed sex with him, so much. He wasn't just bigger than me, he was very dominant. He fucked her with a violence I couldn't hope to compete with. Plus, he could regenerate quickly and go again. I loved it. I was envious of his abilities, but not jealous.
Our three-way relationship blossomed. Watching my friend fuck my fiancée, was all the sex I needed. He was way better at sex than me and I wanted him to be her primary sex partner. So, he ended up moving in with us and we became a poly threesome.
She and I would have sex once, maybe twice a month, while she was having sex with him two or three times a day. However, I stayed very involved by providing clean-up on her and him.
That set the tone for our marriage.