No, but anyone who waits until their SO is unavailable, out of town, or unaware to engage in sexual behavior with another person, contrary to vows or committment they have made with that other person is in the wrong. What 2 people choose to do in the privacy of their relationship is no one elses business. As a wife, I have exchanged vows with my husband to be faithful to each other. I have a reasonable expectation that these vows will be kept. If my SO then dresses, feels like a different person - a woman- and indulges in sexual activity with another man or woman, then he has broken his vows and I have every right to be upset. Same thing goes if he does it in trousers. No one is saying that people cannot practice whatever sexual activity they want. But if you have committed to be faithful to anohter person, then be faithful. It is only if one is in an "open relationship" and has released their SO from that portion of their vows that sexual relations outside the relationship is acceptable.
Dee