Dude, sticky wickette indeed,
1. It's true, and hes freaked by being confronted
2. It's a lie, and shes spreading such things to alienate him form others
3. You can hope that, either way, it registers in his mind and he gains good from it
4.There isn't a whole lot you can do, alerting your parents with info that turns out to be false,,,,isn't a good idea,
5.,,,but, if he's going down that path, you can't ignore it....
Try checking him out, via friends, where he hangs, if you notice any real mood swings, etc (look online for the signs you should look for), and once you have evidence of his innocence, or guilt, go from there,,,good luck
I wish all could find the true happiness I have found,,in the eyes of Mike