Speak the truth.. Fear God rather than men

Therefore do not be afraid of them. Nothing is
concealed that will not be revealed, nor secret that will not be known. What I
say to you in the darkness, speak in the light; what you hear whispered,
proclaim on the housetops. And do not be afraid of those who kill the body but
cannot kill the soul; rather, be afraid of the one who can destroy both soul and
body in Gehenna. Are not two sparrows sold for a small coin? Yet not one of them
falls to the ground without your Father's knowledge. Even all the hairs of your
head are counted.So do not be afraid; you are worth more than many
sparrows.

Matthew 10:26-31

From CCF fellowship:
We shouldn't be afraid of going against people when we know we
are on the side of what's true and right, for men can kill the body, but God can
destroy both body and soul.God can avenge for us against our enemies (Hebrews
10:40-31), for we are precious and valuable in His eyes. People couldn't care
less for they are selfish, but God cares.

We go through life learning that sometimes, we have to resort to doing wrong things to be able to gain the confidence of other people.

Example of this is when a person tells you something slanderous about another person. Because we're lost on the thrill of knowing something juicy about another person and at the same time not hurting our friend's feeling, we tend to encourage such behaviour by contributing more anecdotes to sort of "support" the friend.

Deep inside, you know that this friend has told you these slanders because he is afraid to confront the person he's talking about. Or that, he knows in his heart that he has no grounds over what he feels and is afraid to be confronted back by the other person.

Be a good friend instead, and be on the side of what's true and right. Encourage him to talk to the person instead of talking to you. If he says he just doesn't want a confrontation, then it's because he's still consumed with hurt and anger. Advice him then to let it go, since he's only hurting his self. Those angry thoughts he keep remains in his mind until he lets go. So that whatever the other person is doing, he's taking it against himself.

Flee from temptation to gossip and slander so as not to fall into sin. Guard your tongue and stop before you hurt somebody. What if this other person is also your friend or who treats you as a friend? In the middle of your conversation, try to place yourself in this person's place, and maybe then you'll feel how it is to be betrayed.

How many times have I find out about other people who masked their selves as being "friends" only to hearing them later telling slanderous things behind my back. These people treat confrontation as sort of last resort, because they intend to hurt the other person more instead of clearing the air and resolving the conflict.

Yet sometimes, they're just not your friends, they just keep the relationship going because they get something from it, like companionship, connection etc.

What you can say in the dark, but can't say in the light, is not of the truth but just an ugly and evil thought.

If you are in a relationship where most of the time, you are forced to walk on eggshells and do wrong things instead of being true and right, then slowly let go of that relationship. Cut it off rather than fall into temptation.

If you can't, then lower your expectations and keep in mind that your friend is destroying the trust and respect this other person has given him. If your friend can do this to other people, most likely he's doing the same thing to you behind your back.

Don't be afraid to speak the truth, knowing that you can lose your friend because of this. As Dr. Seuss has said, "Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind."

God will give you people who will be able to stay true and who knows how to let go. These are the people who remember the good times and who can accept you for who you really are. Believe me, they exist.

Everyone has faults but God will teach you to accept each other.

You'll know your friend is such a person if after you spoke the truth, he'll be able to accept it, swallow his pride and realize you're giving him a chance to repair his self and his relationship.
Again, no one is perfect. Your friend might not like it and will go on to the next person who can lend an ear on his slanders. But you have done what's right, you have said what's true. And for now, it's your turn to let go and let God.