You can love your friend and still say they were wrong. Both are allowed.

Loyalty often gets defined as agreement, which leaves a bad choice: back a friend when they are wrong, or feel like you walked out on them. Those are not the only two moves. You can be squarely on someone’s side and still tell them the thing nobody else will, and the telling is part of being on their side. Agreeing with everything costs less and is worth less.

If a friend did something you think was wrong, say it to them before anyone else. Start with the part that is true, that you are not going anywhere. Then say the hard sentence once and stay close.