Why the fuck won't he leave me alone?

[Helen]

Unfortunately, that is the risk you take when you broadcast your personal information to Joe Public.
However if you're using a fake name, then how does he know it's your account? If it was linked to your blog and available for anyone to see, then he wasn't out of his rights to read what was posted in a public domain.
But in the meantime, try to let the immature teasing go over your head. He's obviously very unhappy with himself, because he feels the need to victimize you in order to make himself look cool. He's probably very insecure and desperate to be liked. If he's trying to provoke you, don't let him. Keep your cool and he'll realise he's not getting to you. If it gets much worse, then tell your teacher.
In the meantime, it might be an idea to delete your blog and your Twitter account, if you want your privacy. But if it's a stress release for you, and you don't want to lose the friends you've made on Twitter, at least create a brand new account with no way it can be traced back to you.