I have OCD, I need help, rational thoughts, in relation to STDs?

[Brad J]

I need some rational thoughts on one of the many situations that are causing me to stress in day to day life because of my diagnosis of OCD. I found out one of the guys at college had unprotected sex with a girl he met in the gym in the disabled toilets. I asked him if he used a condom and he said something like 'no, I don't believe in condoms, I want to share if I have something' - he said it in a joking way, but it was obvious he doesn’t wear them. I'm just afraid of being in the same class as someone who has unprotected sex, especially seeing we're doing a fitness course which requires physical contact with this person directly and indirectly on a regular basis. Do most people have unprotected sex? This is also unfair to his current girlfriend who doesn’t go to our college, he was like 'that’s the way I roll', and so what if he contracted something then gave it to her, there isn’t much I can do for her though. Are my fears rational, and is there anything I should do? Thanks