I know trans people and spouses of trans people who have done this. Typically, one of them will come out and begin transition, but the other is 100% straight.

I know trans people and spouses of trans people who have done this. Typically, one of them will come out and begin transition, but the other is 100% straight. They don't want to divorce, since they're still in love, but one of them isn't going to be attracted to the other anymore, so they agree to an open relationship so they can continue to be sexually satisfied while still remaining a couple.