You have unprotected sex with a partner.?
You should talk to your doctor and both of you get tested. In the case of exposure to HIV for example antivirals can be administered to reduce the chances of becoming infected. If that happened to me, that person would cease being my partner and would be completely cut out of my life. Such a person is either evil or an absolute moron, regardless of which they arent fit to talk to me let alone be in a relationship with me.