My boyfriend is on ART and have been having unprotected sex for over 6 months now. I tested HIV negative, could it be that I am still in the window period?

Now that you know, insist on using a condom at every sexual intercourse. It is possible that you are still in the window period. You will need testing at regular intervals for up to a year from the time of your last exposure. Your doctor or HIV counsellor should be able to explain this in detail as per the protocols prevalent in your region. It is also possible that your boyfriend’s viral load is low to undetectable because of the ART that he is taking. In such a case, the chances of transmission of HIV from him to you would be very low. It is possible that you have not been infected. However, you will need further testing in order to be absolutely sure. In the meantime, I would advise you to practice safe sex, use condoms and not to share toothbrushes and razors with him.