HIV medications can get someone's viral levels to undetectable levels. The virus is still there though - HIV hides in immune system cells, specifically in central memory CD4 cells. As long as he continues to take his medication though, he's probably going to be fine.

We're at a point now where drugs like PrEP can reduce the risk of getting HIV from having sex by upwards of 99% (as in, in MSM cases, there has not been any observed cases of HIV during the trials, though in clinical practice there have been a few confirmed HIV infections despite adherence to PrEP). Note that the clinical trial cases involved HIV patients that were also taking medication (known as virally suppressed), so the few confirmed HIV infections from clinical practice could be from partners not on any HIV treatment and with detectable/high viral loads. My point is that the combination of PrEP and HIV treatment adherence could effectively (but not certainly/definitively) eliminate the risk of contracting it.