Just do stuff. To fix the mind, you have to keep busy. Don't focus on yourself, focus on projects. The long history of humanity, the last thing people did until recently was think about themselves. Stop. Do things.. basically touch grass.
As I see it, you can either deal with a problem on your own terms or you can let it eventually deal with you on its terms.
I also lost a dear friend to suicide and he was very succesful and active on his field when it happened. Nobody saw it coming.
It's just not that simple.