Depression Supporters Support Group
This community is dedicated to spouses, children, relatives, co-workers and others who are actively supporting someone suffering from depression or other serious mental illness. Depression can bring about intense sadness, melancholia or despair that has advanced to the point of being disruptive, which can have a grave impact on the ability of others trying to help.
Honestly, the first thing I'd do is look at his schedule and cut what he can from it. Delegate! Pass the community college class off to a sub for two weeks, give up the sound production to someone else, cut out his involvement with the (smaller, uncritical) details of the wedding. Whatever it takes to create some "space" around him.
Then, since he is taking days out anyway, get him out of the house and into a new environment for a day or two....personally, I'd go to on a hike or to the beach or somewhere with minimal people and lots of nature. But maybe his place is a museum or something.
And just be in the moment with him. When he starts freaking out, just say that everything is taken care of and it will be there when he is ready for it. Everything will be ok because you two are getting ready to start a beautiful life together and you are going to support him through this rocky time (for better or worse, right?).
If it were me in his situation and I was so overwhelmed with life that I was shutting down, that is exactly what I hope my Beloved would do for me.
You two are doing all the right things to help him through, going to doctors and getting on meds, take comfort in that. Maybe get a blood test to see if his vitamin D is low...that's an easy fix and can make a huge difference.
And on the flip side, don't forget to take care of yourself!
Good luck and blessings...and congratulations on your wedding!