Re: Were there any people having open relationships in Trek?
Phlox on Enterprise is probably the closest example. He has 3 wives, who each have 3 husbands, who in turn have 3 wives... apparently into infinity, and says he has several dozen possible partners in this arrangement. And he seems to consider Ensign Cutler's suggestion of an extramarital relationship.
Also he enthusiastically encouraged Trip to respond to his wife's sexual advances in "The One Where They Get The Neutron Microscope"
i hate everything