Is sadism caused by a mental problem?

I would like an actual medical article answering this. because I'm just getting confused looking at all this stuff that i can't seam to trace back to anything definitive. It's not like I actually want to go around hurting random people, just my boyfriend and that's not that big of a deal because he likes it but I've sean things on shows like Criminal Minds and I'm alittle scared I could end up doing something like that. Something published after 2008 would be great that way I can use it for my homework to,