I'm not sure what made him change his behavior this year, but it is possible that it's related to hormones or puberty. That at least would explain some of his behavior. Maybe he doesn't know how to properly express his se.xual frustration. So, it's possible it will pass, but for now, you have a few options. You can try ignoring him or avoiding him, even changing your skyp.e account. You can surround yourself with friends, sort of like a wall. You can confront him and tell him that his behavior needs to stop. Or, you can tell a teacher, adult, or someone else of authority. If he were an adult, he might be in jail right now, so he needs to learn self control now and learn it well. Since he used to be your friend, you probably still care about him, but really it's best for him if he learns self control and how to treat others with respect. He can either learn it from you or from a teacher/authority. In the end, it's best for both of you.

The only thing I can think of is to tell an adult, this is sirius[sp] you need to tell your parents or gardian, I'm sorry I dont know how to help.
Be brave sweet heart, he may have been you're friend and you loved him but you need to tell an adult, this can be dangerus[sp].
For thretning[sp] to r.ape you he can be put in prison/juvi

Tell your Mom or Dad