If you are a nurse, Doctor, counselor or social worker of any kind and the patient is a minor, under the age of 18, in any dangerous situation. Either a danger to themselves or someone else, or being abused, etc. You, with the profession you’re a part of, are required by law to report it to the police. Even as a friend, neighbor, bystander or just a witness, you would be helping this person, even if they don’t realize it at the time.
In order to contract HIV, infected bodily fluids have to enter your system. Considering this, having sexual intercourse without a condom would definitely put you at risk for HIV if your partner has it.