If you are hiv positive you have to tell your partners before you have sex. Do you believe this is okay? Even if its "undectectable hiv"?

This is something ive thought about here and there. My mom has a gay friend who has HIV from being raped in his teen years by a man who was an IV drug user. This friend has tried and tried to find someone to care about him and love him but its hard because every person is so put off by finding out he has a disease. His HIV is undetectable, it means that they have reached a point of which their virus is not detectable by modern lab tests and they are not going to transmit the hiv virus. He wishes there was less of a stigma around it and that more people know and understood. My mom believes that those who are undetectable shouldnt have to tell their partners until and if they are ready to. What do you think?