As per the game rules, if you share your account, you will be held responsible for any actions that occur through your account.
citoj:4.2 Member accounts are non-transferable. Registered users are responsible for any actions that take place on their accounts or private messaging systems.
Additionally, if you share your account with a banned player, you will be banned too.
Bottom line, don't share your account. If your "friend" does something and gets your account banned, we will not undo it, and we will not refund any premium days you lose as a result. It's not worth the risk.