How can I protect myself from a spy?

Hi, I'm 17 and recently my 34 year old brother (dad's side) moved in, and well, i'll spare you the drama- I'm no longer speaking to him. this morning there was a bad argument, because I didn't say good morning which ended with him threatening me and my dad warning him that he had no right to do that and it will not be tolerated- and i ended up on his computer which he left on, and i found text files with my usernames and passwords to my myspace and facebook accounts, as well as to accounts I don't even remember having. Apparently he used "cain and abel" password cracker. Before this he had radmin server on my computer, and all computers in the house, so if i'm connected to the internet he can watch my screen and even control it. I've changed my passwords, deleted the text files from his computer, and now i'm going to clear my saved passwords on internet explorer and firefox. My question is- is this enough to protect myself? he's a computer repair tech who recently became interested in "ethical hacking" although obviously he's dropped the ethical part. I just installed norton antivirus to check for any keyloggers. How can I protect myself? my files, my conversations with friends- how do i keep that safe? He's on the network, does that give him easy access to my computer?