A few days after World AIDS Day and at a time when health experts are reporting that there are a whole lot more new HIV infections than previously thought, it's probably a good time to bring up the topic of condoms.
A lot of writers worry about introducing rubbers into their stories but there’s no hard and fast rule.
Some publishing houses take the view that their books are fantasies and who would fantasize about condoms? So they don’t require it. Who wants to think about sexually transmitted infections when they're getting their groove on?
Other houses, concerned about any messages they may be sending about unsafe sex, require writers to, at least, mention that their characters are using condoms. How the writer chooses to introduce the topic is up to them. It could be a one liner where a character mentions using it or discarding it after sex or it could be something lengthier where putting it on becomes part of the sex play.
So whether you choose to condomize or not really depends on the writer and their particular publishing house. I don’t mention condoms in The Gladiator’s Woman, not because they didn’t have condoms in ancient Rome, they did, but because it being a historical I didn’t feel the pressure to do so. People just weren't as worried about those diseases back then and there was a lot more ignorance about signs and symptoms. In a contemporary, I probably would bring up condoms. In another life, I was an HIV educator and I'd feel I owed it to my readers.
What you do depends on you and on whether the publishing house you're targeting would allow it. If you're unsure, look up the guidelines, read other books they've published, or, just ask the editor.