Hi Ali, I think you have just got to concentrate on all the good aspects of having what you wanted back again. You did say his depression didn't affect your mood, although I think it must to some degree.
He has had it since he was early twenties I think you said,in all likelyhood he will always have those tendancies but it is just more at the fore at the moment,coupled with all thats happened and this guilt you talk of. You are strong and must just rise above all the "distance" It will get better.
I thought he had gotten some AD's, maybe he needs more than the supplements. I am not an advocate of them but have seen remarkable changes in some people and therefore their lives to know that they can have great results.Maybe worth giving him a nudge.
I loved the icefloe analogy,very poetic. Talking of which it has just started snowing!
Got any party plans or visits that will do you both good,enjoy the season.