I am so very, very sad and sorry for your loss. This is horrible news, and my heart goes out to you and your family.
When you originally posted your family's situation I was hugely heartened to see a parent so willing to help a child deal with gender issues. I still think that what you tried to do was motivated by a deep care and love that is sadly absent in many parents.
Your son was a fragile being, and he imposed a terrible pressure on himself. I wish the outcome could have been different.
As you seek to move forward there are not many answers, just ways to cope with the loss. Although I am not religious, my nominal religion, Judaism, offers a highly pragmatic structure for coping, mourning and evolving, at a time where so much existing structure has disappeared. Perhaps it may help, along with some grief counselling.
Our thoughts are with you.
Julia