Slavery: A series of erotic games (book 01)
"Harold and I realized we were no longer capable of giving each other everything we needed from a partner. We still loved each other, but something was missing. There was no mystery anymore; no surprises. Since we still loved one another, we didn't want to get a divorce, so we decided to just open the marriage and let other people in, though I don't think either of us has gone so far as to engage in any homosexual behavior, have you, Harold?"
"Nope, strictly ladies for me, though I did have a threesome with another fellow and a woman. We didn't really touch one another except accidentally," Harold answered.
"Just men for me. I had a threesome once myself. Quite the night," Mary reminisced. "