In order for a ban to occur, there must be proof first that he was the one who did this. Otherwise, there is a chance the admins would be banning a player for no reason.

Sometimes people give their passwords out and get duped. Othertimes, another player is able to figure it out on their own (maybe because they know the person well enough to guess their passwords). But you should never give anyone your password and you should make sure yours is not easily figured out. Perhaps your friend was using a very standard password, such as 'abc123' or even 'password1'.

Either way though, everyone should be cautious and make sure to secure their accounts. Never trust anyone to enter into your accounts. Anyone who can legitimately help you can send whatever you need by other means.