Over-explaining
The instinct is to flood the other person with information. This backfires. Tell them the basics, then stop. Let them ask.
Apologizing for existing
Disclosure is a fact, not an apology. Stay neutral about your own diagnosis. You did not do anything wrong.
Disclosing during sex
Bringing it up while clothes are coming off creates pressure, panic, and bad decisions. Disclose in a calm moment.
Not having a plan for protection
Be ready to talk about how the two of you will handle protection if they want to continue. Condoms, suppressive antivirals, PrEP, vaccination — know what is available.