Being the middle man is no fun!
Take this for example: Your best friend's husband is having an affair with a work colleague. You know about it, and ponder over whether to tell them or not. If you don't and they find out you know... they will never speak to you again. If you do... well, that's another story. This mostly results in a big fight with them and their partner and then they make up, but with you being the person who was the bearer of bad news, the "dobber", and the one that one of them can no longer trust.
It's a no-win situation.
And this: You are out with a group of friends, and a girlfriend/boyfriend combo is with you. One of your friends talks business with the boyfriend, and plan to catch up. They catch up, have an attraction and eventually start a relationship. Boyfriend dumps girlfriend for your other friend. Messy. Girlfriend never speaks to you again for "setting them up".
Then there's: You are doing business with someone, and one of their staff members starts referring you clients. That staff member dates one of your friends, and then breaks up. You have no issue with staff member, and as they move jobs from one to another, they keep referring more clients. For the sake of your friends breakup - do you keep accepting new clients?
The world is a crazy place. Shit happens, more often than we care to admit. As long as all parties are honest, its a fine line as to whether you share information that you are 100% certain of or not. To be totally honest, mostly I choose not to. It always ends in disaster. But a few times, you have to think about whether or not you would like to know the truth, and if the answer is yes, and you know for sure that that person would want to know - you have to take the risk.
I try not to share information that has no other result than to hurt someone's feelings. If someone says something bad about another, don't tell them. Why do you need to ruin their day just because someone else is clearly insecure about the person they are slandering? It's as simple as that.
Being the middle man is not fun, and there is never any reward. It is a place that allows everyone to pound you with balls all at the same time, or worse, fire you!