And about the 'not completely understanding'... I can relate. I would imagine it is a somewhat common feeling for people with depression.
My OH studied psychology, and he understands (in theory) what it is I am up against. But it is never quite the same until you experience it. He hasn't had depression or anxiety (although I do think he sometimes gets down/ temporarily "depressed", but doesn't have the illness).
It can feel lonely, when in a relationship with someone who doesn't 100% 'get it'. But that is neither their fault nor yours.
Don't try to be *too* perky, for your own sake. I know you want to try to make it easier on your wife, but it can be a strain, tiring to be cheerful and also difficult because you feel like you're being dishonest about how you feel.
I was doing that at one point too, and I just got so exhausted and I broke down in tears one day and said I couldn't handle trying to be cheerful for me and him both (because he isn't a very extroverted person, which is fine, its his nature).
What you are going through is a tricky balancing act - looking after yourself as you fight depression, and also not wanting to let your wife have to deal with it too much. Pat yourself on the back, you are trying really hard.
A suggestion would be to encourage her to spend time away from you/ home from time to time (if she doesn't already) with her own friends etc, as she needs a network of support as much as you do.
Keep us updated, hang in there!
*)*