If you’re feeling depressed, you need to think about something else. I remember seeing the move Old Yeller, and later reading the book. The young protagonist had shot his rabid dog while his father was away and his father came home to talk to him.
Guilt and grief together are the hardest to deal with and the father, with his experiences in the Civil War seemed to understand this. He told his son that the best thing he could do about it was to forget about it. He said he understood that sometimes with things like this it was hard to forget and that you might feel like you don’t want to forget about it. He followed that with the observation that there are a lot of good things in the world and if you just concentrate on the bad things, it takes away from all the good things.
Life is too short for constant sadness. Cheer up. There’s a lot of really great things to see, people to know and experiences to be had.