Hi, I just happened to stumble across you post when I goggled "depression spouse." Yours was at the top of the Google list! I have been married for almost 25 years. My husband has been depressed off and on, now mostly on, during all these years. He has been seeing a psychatrist for 18 months, with little improvement and he is currently on a low dose of Lexapro and has been on Effexor in the past.
That said: yes, becoming a hermit is normal. Getting ready for work, going to work, and being at work and trying to appear as normal as possible, trying to do the best they can so they don't get fired....all of this takes a tremendous amount of emotional energy. When he gets home from work, he disappears inside of himself. The depressed are so emotionally spent, they have no reserves, nothing left to give.
My husband sits in one of his two "chairs" and reads while watching TV. He watches two shows at a time so there is never a good time to talk to him. His chair is in the corner of the room so no one can approach him, touch him as they pass, and he can't hear you unless you come to him to talk.
As for socializing, one a month is tops for us. We used to entertain friends for dinner at our home once a month. Now, never. We see the same group of friends (3 other couples) once a month for dinner. He knows when this is scheduled and is "on" when he walks in the door. He is "off" as soon as we walk out of the door.
What you are experiencing with your husband is normal behavior for depression. How long has it been going on? When was his last episode? Has he recently gone on/off any meds? Has he even seen a doctor about this?
I would recommend you read the book "How You Can Survive When They Are Depressed."
Remember, it's not you. And, it might not ever be better than it is today. I am trying to decide if I want to spend the rest of my life like this.