Hi Joel,
Have you checked South Carolina law as to how to legally change the locks? Make sure you do before you proceed.
As for the security deposit read this link to South Carolina law:
http://www.scstatehouse.gov/code/t27c040.htmAccrued rent may be deducted from the deposit. Make sure you fulfill any notification requirements after move out. When did the lease start and when does it end? You may also be entitled to rent through the end of the lease or when you re-rent depending on which comes first. It doesn't sound to me like this tenant will be getting any of the deposit back.
And yes think happy thoughts. Don't get discouraged, there is a great tenant out there for you. You just need to bone up on some things and stop being such a nice guy (when it comes to renting). You can be both a good guy and a landlord, just put
your pocketbook and family first.
Hang in there!