Not me, though I did once have a bisexual girlfriend. Something I had no issues with, though my indifference and acceptance of it eventually seemed to contribute to a rift in the relationship. She once asked if I would object to her having on rare occasion experiences exclusively with her cousin (married to a man) and it didn't bother me. Though I never met her cousin either, who lived in another state.
To me she wasn't "cheating" but rather just getting something out of her system. I guess she
wanted me to be jealous of such things, and jealousy and envy for whatever reason (not likely ASD) just don't happen with me. It always left me confused. I just didn't consider it within the parameters of an open relationship. Especially on such an infrequent basis with only one person who was of an alike mindset. Maybe that was my mistake.