This is sexual abuse, but a great fantasy. I would respectfully suggest we talk about this in those terms, rather than discuss potentially illegal things publically in an open forum. (Never know when the FBI is watching, and ironically they're cracking down on Internet Predators to distract from the creepy uncle in chief.)
I write about this a lot, but typically target Child Molesters/pedophiles, so not with any stories on this board. Age Play has eliminated one of my submissions from being published, so I'm just avoiding the issue of Consent all together. Too much time, and emotional investment goes into my stories to risk publication, because of the standards of Literoritca. I just follow them.
However, fictionally, and hypothetically, that's the ultimate target. For age-appropriate LGBT, the more reliable ploy is a straight woman blackmailing a gay man under threat of outing him, for femdom. (Okay, a straight guy can try this with lesbians, but homophobia is much more powerful a threat than Sapphobia.)
Another good story idea is a Bisexual husband, or wife, and a homophobic spouse. They want to keep their secret safe from their family, and may threaten to leave the Mistress/mister to prevent a divorce. So, the extramarital lover could blackmail them for sex, and escalate to all the stuff the married lover wasn't willing to do before. (Anal, BDSM, Exhibition/Voyeurism, Picarism, castration play, and Rape) knowing they won't dare leave, or report the relationship.
I would probably do a proto-familly Annihilator, with a gay/transgender lover. They typically gamble, drink, and'or get addicted to prostitutes, but when threatened, commit mass murder/suicide (Hence the name Family Annihilator) to "Save" them from their delusional worldview crashing down.
Another possible motive is financial. (It's usually a Looming Financial crisis, like losing a job, forclosure, and/or hidden debts being discovered in Audit) However, instead of the queer lover blackmailing them for hush money, a twist could be a straight boss, like a bank manager, being blackmailed for sex by an underling, with mobsters to back it up. Money Laundering, yeah if his wife found out, she wouldn't literally Kill him. The FBI could apply pressure, but the Mobsters/Cartels he's cooking the books for him can get rid of his body.
He'd do anything to avoid that. Hope any of these help...
I know what I think. Ask, don't assume. Denial doesn't change anything.
Exception: I am not interested in being solicited by men on the internet who "Always wanted to fuck a tranny." Don't bother asking, the answer is already No.