I completely agree with Leed. I would report it. It's illegal, and nipping this in the bud might save some little girl's life somewhere down the line.

It's sick. Run as fast as you can. And I'm going to sound annoyingly old here, but it's highly unlikely that you're going to stay with, marry, and grow old with the boy you're dating at 17. I know it's possible, but just not likely. So why not fast forward and move on to someone better?

Yes, everyone has fantasies, but that's not a fantasy, that's sick. And it could be a good indication that he might become a very dangerous man.

Good luck! This must be an incredibly difficult situation for you. But I'm glad you snooped around his computer. This can't continue.