I don't to share my diablo 3 with my brother so does diablo 3 only sticks with one account? If it does I am so grateful because I don't want anyone touching my diablo 3.
Also will it only stick with one account and you can't make any others or else you won't be able to play it unless you buy another CD code for that account?

I'd say only 1 person would be able to play the game at a time definitely.

My best guess is 1 purchase of the game equals 1 account so lets say you can have 5 characters per account, you and your brother would have to take turns playing and would have to share those 5 character slots.

If you want you and your brother to play on separate accounts you would have to have 2 copies of the game. You have to log in to battle.net to play it so just don't tell your brother your password and all should be good.

i believe that both are correct just have to buy another copy of D3

Yes buy another D3

1 person per acc, so if 2 online at a time youre gonna need 2. no sharing of accs as far as i know apart from seperate chars

Yea you won't be able to both play I don't think..