Charlie Sheen's former nurse, Amanda Bruce, had unprotected sex with the HIV positive actor for months before he dumped her (as he does with all his women). Sheen, who is very good at making women believe he loves them, when he does not, convinced his nurse to have unprotected sex, though she knew his HIV positive status and that she would be endangering her life. Bruce thought she was in love with Sheen, who was using her for unprotected sex, something many women would no longer consent to, due to his status.
Bruce took medicine, PrEP, which stands for Pre-Exposure Prophylaxis, to reduce her chances of becoming infected with HIV from Sheen. However, it was an unsafe thing to do, as drug manufacturers warn against unprotected sex even with the use of anti-HIV medication. Drug manufacturers continue to correctly emphasize there remains a risk of contracting HIV from an infected person, with or without protection, when on their anti-HIV medications (which also have very unpleasant side effects that are not easily tolerated). Hence the phrase "safer sex" not "safe sex" as truly, it is not safe.