1 Help, Yahveh, because there is no faithful one left; the loyal ones have vanished from the human race. 2 They lie to one another; they speak with flattering lips and deceptive hearts. 3 May Yahveh cut off all flattering lips and the tongue that only says great things.
Is my tongue faithful? The psalmist is talking about those who refuse to be honest in their assessment of others. No doubt some who are like that hide behind the idea that criticism is unchristian. They refuse to say anything negative. They tell themselves that they should build others up, not tear them down.
A faithful tongue respectfully tells it like it is. The psalmist laments the loss of such friends. When you cannot trust your friends to tell you the truth, you have lost your true friends.