Don't. Ever. People trust you and tell you things based on this trust. If you tattle tale the person you're telling and the person you tell won't trust you again and you risk putting yourself in the middle of a messy situation. If you know something damaging about person A that would impact person B - ask person A why they told you and/or tell person A to tell person B. If you do tattle tale then be sure to tell the person you tattle taled on asap what you said and to whom.

Our rule with our two kids works equally well with adults. If you're trying to decide whether or not to tell someone something (their wife is having an affair--they might be getting fired--you know their boyfriend has a sexually-transmitted disease--whatever), apply the following criteria: 1) Is someone physically hurt, or about to get physically hurt? 2) Is something damaged, or about to be damaged? If either situation applies, you should tell. This helps winnow out the useless-but-fun-to-tell gossip from stuff you really should feel honor-bound to tell someone. If neither of these things apply, zip that lip!

Consider whether or not things will get better if you share the information. And remember that someone will be angry with you so you need to decide if its worth the possibility of losing a friend. Sometimes tattling can be the right thing to do but your friend (or friends) may be angry with you for a few months if the truth is hard to hear.

Look to your motives: if your motives are either selfish or borne out of your own insecurities - don't say a word. Should you do so in those circumstances, any perceived gain will be shortlived and to the detriment of your confidence and self-esteem. If however your motives are true and respectful of the other party (there has to be no doubt in your heart), tell them honestly.

Its the classic, what would you do if it was you? If you knew your friend knew your bf was cheating, would you wish she told you? I like to keep out of tattle tale situations because if it goes wrong, such as they break up and he wasnt cheating on her, or if you knew and they didnt break up, you could be classed as the "bitch". Unfortunately where I live its a very small chinese whispers kind of town. My best friend told me he heard of someone who heard off someone else my fiancee was cheating, later confronting him, it was his half sister and niece! Luckily it was a misunderstanding, what we over looked, and didnt argue or blow up.

Don't! You expect your friends to trust you and if they find out that you told someone one of their secrets, I doubt they will be very happy with you. The only exception would be if the secret could lead to someone getting hurt, for example if you knew a friend was being treated badly. Even before you do tell, try to pursuade her to first, and if you can't do that and decide to get help for her, reassure her that you were only looking out for her and doing the right thing.