I'm so sorry your son is going through this. Depression is a terrifying ordeal for all involved. You have my best wishes and healthiest hopes for your son.
Is there a writing group--possibly for college students or adults, since he may not fit well with kids his own age--that he could join?
I guess what I'm saying is that I would focus more on finding groups that do the things he likes to do for the sources of friendships and less on the ages of the people doing them. He may do better that way. A highly sensitive HG teen often has trouble finding friends among same-age peers. It is actually very normal to have that kind of trouble. He's not a weirdo: he's just a normal gifted kid!
And I'm with 'Neato--make sure the therapist understands GTness and how that is affecting his condition. It matters.
Finally, I don't know enough about his school situation to advise you with any confidence there, but it does sounds like some thing(s) there are not working for him. It might be smart to talk with him about what specifically is wrong at school and what options you can make available to him to solve the problems. Encourage him to turn outward for this conversation instead of inward. You want him to be angry or frustrated or to place blame on others, not to blame himself. It sounds to me like at least part of the reason for his depression is because he thinks he's the whole problem. If he sees that the situation is the problem--and you can make changes to the situation!--maybe then he can feel better.
But with that said, know that I'm just a mom with some personal history with people with depression, not an expert. Depression is a serious medical issue, so be smart about taking care of him! Follow doctor's orders and all that! (As I know you will!)
