If they have unprotected sex with you and they've tested positive for HIV and don't tell you, it's murder. I'd press criminal charges AND file a civil case. If two people had unprotected sex....wouldn't two people be to blame for transferred diseases?
Yes, they owe it to you to be honest about any diseases....IF THEY KNOW...but you also owe it to yourself to use common sense and protection if it's someone you may be at risk with. If you don't, you are as much to blame as them. Why the hell would you take that risk?