I also imagined doing some really bad things to people that have caused me pain and made me into what i am today i even imagined ways of doing it to try to avoid getting caught, i even thought about doing it for real, but even though i feel that i could do it if a wanted without feeling a thing i know that murder or torture (i did both in my head) are not right so i won't do it. It would also be bad if things turned bad and i ended up arrested xD

Anyway you should dispose of that diary, its not good to have something like that with you, you can get into trouble because of it.