PEP regime is basically a drug cocktail that would block formation of certain viral enzymes to refrain the virus to replicate. Thus, eliminating the process of infection. Truvada consists of 2 drugs namely, tenofovir and emtricitabine.
Before 2013, PEP was recommended with this 2 drug composition. However, after 2013, three-drug regimen consisting of a nucleoside reverse-transcriptase inhibitor (NTRI), (tenofovir plus emtricitabine), along with a third drug, either an integrase strand transfer inhibitor, raltegravir or a boosted protease inhibitor, darunavir/ritonavir is recommended for PEP.
Ideally, NTRI is an important component of the regimen because if HIV infects a cell, it first attaches to and fuses with the host cell. Then the viral RNA is converted into DNA and the virus uses the host cell’s machinery to replicate itself during a process called 'reverse transcription' this drug can simply block that above highlighted process. Therefore, the infection can be terminated in most cases.
Some doctors feel that tenofovir-based two
drug regimen are more likely to adhere to post-exposure prophylaxis than discontinuation due to strong side effects. Perhaps, that could be the reason for prescribing just the Truvada. You would need to follow up with your doctor to find out the answers to go with whether 2 drug or 3 drug regimen because no one here online or on any other website can substitute a doctor's advice.
I also want to highlight the fact that if your partner suspects he is HIV positive, he can go and get himself tested now to save you from this ordeal and if he is aware that he is HIV positive, despite of that knowledge, he didn't insist on using protection means a deliberate attempt to jeopardize your health, in this case, you do have the option of approaching your local law authorities.
Please describe your risk clearly for us to provide you with better support.