I've been a Christian for a very long time (since I was a kid), but it wasn't until my early thirties that I read Joyce Meyer's book, Battlefield of the Mind. Prior to that I thought that every thought that came into my head was mine, and I'd wrestle with each one since I thought it's meaning and root was something in my soul. When I learned that the enemy (Satan) has access to (for lack of a better term) shoot, like arrows, thoughts into my mind... I started to look at them much more critically.... the imposters became more and more obvious: "This isn't mine, it's an attack." That has helped me tremendously in life. I know this won't bring his friend back, but maybe it will help with the struggle to understand. Many people have no defense walls in their lives. The enemy ransacks their kingdom (their mind) over and over. His friend very likely didn't know how to explain or ask for help. I can't even imagine what he's going through. I echo the advice to just sit with him, like a faithful dog would do. If you're not yet comfortable praying with him, you can pray for him. It WILL make a difference. Your son's relationship to God is your highest calling. Do battle for him regularly in the heavenlies. You'll be amazed at God showing you how he'll answer.