Perhaps it's both ptss and depression?
Lucas, you really can't blame yourself for feeling that way. For one thing, you're stressed out of thinking about A LOT of things.. I admire you for being mature at a young age, and for standing up for your brother, despite all that's happened.

What if distract yourself from feeling that way? Like bond with your brother, play together or something? That way, he'll be reminded more of your fun times together rather than seeing you worried and blah. ;]

<font color="purple">Clandestine</font>