Always take advice on the internet with a grain of salt - mine included - but I'll say the following:

You sound like you've had a tough time. You are being very hard on yourself in your post.

You say your doctor came to the conclusion you were depressed before he died. Go talk to another doctor about it. You might have to talk to more than one to find someone good; but find someone good that listens to what you say.

Maybe get them to refer you to someone that will do talking sessions with you so you can talk out the issues you wrote about, and start to process them.

Talking this stuff out, with someone who is good at this process, is something that helped several techies I know get where they want.