Once someone falls out of routine and becomes inactive, self-esteem and habits go too, the OT will try to rebuild these.
Can I be really frank?
Most OTs, psychotherapists, psychiatrists and especially nurses are totally sh!t at their jobs-sorry, that's the way it is. Most of them are jobsworths, especially on the NHS. Pay close attention to what the OT does, it may just be a load of bs.
One of the most important predictors of outcome for the depressed is social support. You could be the difference between pulling through, and not, for him. I know it is tough, but if you continue to be patient, it should reap rewards.
It's very difficult for most depressed people to open up and interact, but it depends on the type of depression he has, and what caused it (trauma, a purely endogenic brain chemistry malfunction, etc). What drugs did they give him? Does he have any other separate anxieties or problems that you know of?
Chin up love, hope it works out.