The non-offensive word I have seen used for a person who seeks out relationships with homosexual people despite being the opposite gender is “beard”. This is derived from the fact that it helps the male in the relationship present outwardly as a “real man” with a “normal relationship” in settings/societies where homosexuality is not considered acceptable to one degree or another. Also, sometimes homosexual couples of opposite genders will “beard” for each other in a mutually-beneficial dynamic.

edit: it seems spoiler text doesn’t work right on a lot of mobile apps, including voyager. Anyways: watch For All Mankind. It’s great.