I'm mad at my roommates for hooking up
Your roommates are getting it on?
Yes and I am not into it.
I understand being concerned about your reputation, but how does the legal behavior of what consenting adults are doing in the privacy of their bedrooms affect your reputation? Maybe you should share your concerns with them.
Maybe some people would consider it weird that I'm living with these kinds of people.
Adults can date who they want. I doubt people are talking behind you back about having roommates. They might be jealous about how low your split of the rent is.