allthewayanimeIn a letter which one of them should I use: dear me or dear myself?
Only you will be reading it, so it's your choice! (
me sounds better, in my opinion, but it's still your choice.)
Don't you know your name? For example, if your name is Robert, why not write Dear Robert?

CJ
dearself dear self
Someone raised it up. Nevertheless, OP might want to write a letter to themselves for some reason, but I guess that he/she wanted to send a letter to someone else, and he/she was trying to say "My dear".