Living with a partner with depression can be hell; and the fact that you as the partner are expected to be unremittingly saintly and sympathetic is very hard indeed. And totally unrealistic. You do not stop having needs just because he is ill - you cannot be all give, give, give without beginning to crack round the edges.
I know of what I speak! My DH sadly died in February after years of PD, and prior to (and during) that he was a very anxious and at times very depressed man. It nearly drove me nuts - I felt like shouting "I want to have some fun!!!" Don't misunderstand me, I was not unkind or cruel to him in any way, but it undoubtedly took its toll on me. Every single thing that we did was walled around by his feelings of misery.
At least your OH has acknowledged that something is amiss - believe me that is a huge step in the right direction.
I have seen this from the other side, because I suffered a depression following some surgery - I really know that feeling of utter despair - of feeling so very ill that you just cannot find the energy to go on. So I know what your OH is going through.
I came to the conclusion that the only way I could deal with it all was to make time for myself. To get out and do things that I enjoyed at every available opportunity. I know that this is very hard at the moment because of Covid. I am a singer, and went to every choir going - I ringfenced that time and took every bit of help going with the children so that I could continue to do this - honestly it kept me sane! Sometimes I simply could not listen to the litany of misery any more; but if I knew a practice was coming up I could take a deep breath as I knew that there would be these moments of enjoyment to savour.
I do not know what your "thing" is, but grab it with both hands and, above all else, make it a priority - because YOU are a priority, not just the ill person in your household. When I finished up nursing my OH through his last years, I still sang - I paid people to be with him. I absolutely knew that if I did not make that time for me the whole pack of cards would come tumbling down.
I remember so well when he stopped work because he could no longer cope - he just made the decision, and it was expected that I would simply make up the shortfall somehow!!! It is a big burden.
Do not misunderstand me, he was a lovely man - but he was an ill man.
So.....please remember that you matter. Make a time space for yourself that is sacrosanct and take heart from it. Just because someone in your house is ill, it does not mean that your needs can be jettisoned. In the long run, you are doing him a favour by looking after yourself.