Indeed there is. There is a box you can check at log in that says something like "stay permanently logged in on this computer". I never have to log in. And if he uses your computer regularly he's probably got that setting checked.
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .