Decision to let sick person go

I had to make the hardest decision in my life. My husband of 50 years was suffering from multiple autoimmune disease + bone marrow neoplasm for the 16 years. Last year where constant hospital admission with nearly every organ affected. I was watching him slowly being more and more sick, but his will to leave was strong. I become his carer, but for me it was privilege not a chore. Recent hospital admission, he suffer from multiple organ failure, I have seen him in some much pain and distress, that I ask doctor to help and make him not suffer anymore. He did not suffer, everything stopped, and I stay with him every second, every hour, every day till his end.
Now I am crying all the time, have that massive guilt, that maybe was something else to be done, and I let him go.
We love each other and have been together all the time, and now?
Its so soso difficult and empty.