Boyfriend taking HIV meds...claims neg, says its for bad immune system caused by cancer treatment.

Ive been with my boyfriend for about a year monogamously, and we've been truly together as partners for about 5 months. This whole time i knew he was taking medication. He told me before that a cancer battle in 2011-12 killed his immune system, and he had to take a pill for it. Just recently i realized that pill is Complera, an HIV antiretroviral. Looking it up, i have found no evidence that it has any use outside of HIV...when i confront him, he claims up and down he is clean, and itwas what he was prescribed in 2012 for his immune system.I dont know if i can believe him. What can i do? Im getting tested ASAP. Everything i look up says its used only for HIV. What do i do? Please help me...Im beyond scared.