I have been told the word "homosexual" is "offensive", and that I "should never, ever, use it".

I searched for why it's "offensive", and found some arguments: https://www.glaad.org/reference/offensive

https://archive.ph/muB8X

They say that "homo and homosexual were and are used by homophobes as a slur. They use the word "sex" in homosexual as though it's a bad thing, so homo and homosexual are offensive and should not be used". They prefer "gay", "queer", and "LGBTQA+" because they don't have "sex" in them, and aren't used as negatively as "homosexual" has been and is used.

There are also people who say "homosexual is clinical, so if it has to be used, it should be in medical papers, not in conversations or regular writing".

That five-syllable word (homosexual) has never been more loaded, more deliberately used and, to the ears of many gays and lesbians, more pejorative.

“ ‘Homosexual’ has the ring of ‘colored’ now, in the way your grandmother might have used that term, except that it hasn’t been recuperated in the same way,” said George Chauncey, a Yale professor of history and an author who studies gay and lesbian culture.

Consider the following phrases: homosexual community, homosexual activist, homosexual marriage. Substitute the word “gay” in any of those cases, and the terms suddenly become far less loaded, so that the ring of disapproval and judgment evaporates.

Some gay rights advocates have declared the term off limits. The Gay and Lesbian Alliance Against Defamation, or Glaad, has put “homosexual” on its list of offensive terms and in 2006 persuaded The Associated Press, whose stylebook is the widely used by many news organizations, to restrict use of the word.

“Gay doesn’t use the word sex,” he said. “Lesbian doesn’t use the word sex. Homosexual does.” “It also contains ‘homo,’ which is an old derogatory,” he added. “They want to have that idea there. They want to say this is not normal sex, this is not normal family, it’s going against God.”

Offensive: "homosexual" (n. or adj.)

Preferred: "gay" (adj.); "gay man" or "lesbian" (n.); "gay person/people"

Please use gay or lesbian to describe people attracted to members of the same sex. Because of the clinical history of the word "homosexual," it is aggressively used by anti-gay extremists to suggest that gay people are somehow diseased or psychologically/emotionally disordered – notions discredited by the American Psychological Association and the American Psychiatric Association in the 1970s. Please avoid using "homosexual" except in direct quotes. Please also avoid using "homosexual" as a style variation simply to avoid repeated use of the word "gay." The Associated Press, The New York Times and The Washington Post restrict use of the term "homosexual" (see AP & New York Times Style).

Offensive: "homosexual relations/relationship," "homosexual couple," "homosexual sex," etc.

Preferred: "relationship," "couple" (or, if necessary, "gay couple"), "sex," etc.

Identifying a same-sex couple as "a homosexual couple," characterizing their relationship as "a homosexual relationship," or identifying their intimacy as "homosexual sex" is extremely offensive and should be avoided. These constructions are frequently used by anti-gay extremists to denigrate gay people, couples and relationships.

As a rule, try to avoid labeling an activity, emotion or relationship gay, lesbian, or bisexual unless you would call the same activity, emotion or relationship "straight" if engaged in by someone of another orientation. In most cases, your readers, viewers or listeners will be able to discern people's sexes and/or orientations through the names of the parties involved, your depictions of their relationships, and your use of pronouns.