Covering for a friend’s lie turns it into your lie too.

A lie needs people to hold it up. The moment you repeat it, confirm it, or stay quiet when asked directly, it stops being only theirs and starts being something you are doing. Your friend keeps the benefit and you take on the risk, which is a strange trade to make for someone.

You can be on somebody’s side without becoming part of the story: tell them you will not back it up, and tell them before anyone asks. If you are put on the spot, saying you would rather not answer is not a betrayal. Being known as someone whose word holds is worth protecting.