“I caught my friend having virtual sex online”

Recently I had introduced my friend to a social game online. It was supposed to be something fun that we could do together and maybe goof around with. However, things have taken an unexpected turn. I caught my friend having virtual sex with multiple people online. I’m not sure if they know that I know what they’re doing, but now they’re spending more time going in dating rooms, and having virtual sex with people.

Again, I wasn’t expecting this. I’m just worried about my friend, as I don’t think this behavior is healthy… maybe I’m just a judgmental prick. Also, if it helps, we’re 18 years old…