I haven't gone through that, but I'm really sorry that happened. I can't even imagine how I would handle it. I'm really sorry.
I know if it were me, I would try to learn something from my friend so it doesn't feel like it was all for nothing. Send a text to someone you haven't spoken to, just so they know you're thinking of them. Smile at someone you don't know who seems quiet or sad. You could make alot of a difference to someone you don't even know.
When people lose a battle with depression or anxiety, I feel there is always something to learn from them.
100% this. This has crossed my mind every single day since I lost my friend.