You need to explain to her that if they aren't even dating, she is way too young for a fuck-buddy. The bastard is just taking advantage of her.
When I was 15, my boyfriend was 19. We were married when I was 16 and divorced when I was 18. I'm 37 and have a 21 year old to show for it. Trust me, you don't want that for her.
Were it me that walked in on them, I would have beat him with any picece of furniture I could have lifted, then told the police I thought I was walking in on a rape.
