Open Question: Can HIV suddenly disappear ?

Does anyone know how this is possible? 1.Someone has been tested HIV positive 3 different times, over the course of 5 months and even started treatment (but soon after went off as doctor deemed unnecessary). 2. One year into it, they have been tested negative 3 times using 3 different test types, even though they have continued to have receptive unprotected sex with HIV+ partners over the last year...