It should be in a relationship because casual sex is basically a breeding ground for STDs all of which can cause extreme pain, infection and scarring, PID (Pelvic Inflammatory Disease), infertility and death. Monogomous marriages create a more stable ground and can help prevent the spread of STDs. Think about it: if your partner slept with ten people, when you ingage in such behavior you are exposed to every pathogen that each of those partners were exposed to. It makes sense if you only slept with one other person, it would all but end the spread of the disease.
Trust me on this one, after a through education you learn two things:
1. Sex = Bad / Convent = Good / Sex = Kind of facinating, like a two headed goat, but don't get too close or it might eat your skirt
2. the words 'foaming' 'oozing' and 'vagina' should NEVER be used in the same sentance. 0.0 trust me.