I find existentialism very useful for myself, as a mode of thinking. To be honest, the concept of existential loneliness is something I find both exhilarating and comforting. Or perhaps "exhilarating" is not quite the right word - liberating and validating, rather. When I was suicidal, I found articles like the ones found here very helpful.

I've never read Yalom and my therapy is not based on existentialism, though.