I've posted the story in another thread somewhere, but an ex-wife, her sister, and I had a 3 way one time.
The wife didn't participate for long, and left us in the bedroom alone.
It was great fun, but I would've rather been able to fuck her sis all alone.
Back on topic, I usually think of other guys that have fucked her. Some I know and/or have met, some were before we met.
I love to watch my cock slide in and out of her pussy, while I think of them having that exact same view, and how she had to be loving every minute of it.