It's not about disease it's about a betrayal of trust. It's about going behind your partners back and engaging in sexual activity with someone other then their partner. He wasn't chatting with a friend or a family member, he was engaging in a sexual act with a person outside of their relationship. They don't need to be married. This isn't like asking someone not to wear booty shorts to a family picinic. This is about someone going behind their partners back to dirty talk and wave his danglies at a person who he is not currently dating.