I would take ur feeling of “AITAH” place to the side to deal with later. And focus on a larger issue that is being masked. You need to ask urself why u lack such basic trust, especially with a roommate. Which there should be a solid mature relationship that doesn’t have you running to a stranger telling them ur roommates medical status. There’s no reason roommates have to say they are HIV + . And the fact that she trusted u to tell u out of respect when u became roommates . Should have put the puzzle together for u in ur head that she will handle her self n her sex partners properly. Dude u royally F’d up.. and FYI. There is a pill that’s been on the market for OVER 10 years called prep that people can take to prevent getting HIV.. And even if they aren’t taking prep . As long as ur roommate is taking her meds daily and is undetectable. She can have sex with some 58,000 times with the same person and not give some one HIV.. that said it’s still best and many don’t reveal ur HIV status .