Friend of the friendzoned

Isn't it sad when you're in the same circle and a friend falls for another friend who considers him as just a friend?

So sad that I couldn't do anything. I can't tell my friend to like him nor could I ask him to stop liking her.

What's worse is that all you could do is watch and be there for them while their friendship goes into crumble.

Do you know what to do in this kind of situation?