My roommate and i share a bathroom. i was masturbating one day with oil which then fell on the wet bathroom floor. i then again used the same oil. i am scared about hiv, as my roommate may have masturbated. both of use have never had intercourse?

In the 40+ years of the known worldwide HIV/AIDS epidemic, there has never been a case of infection from contact with a contaminated environment. No sex (and no shared needles for drug use) means no risk for HIV. It doesn't matter if your roommate had HIV or not (but probably he doesn't right?). Also no risk for any other STD until/unless you have sex with an infected partner. No worries!