Trust in friendship does not exclusively mean trust in the truth of your friend's statement. It also means reliance on some quality or attribute of your friend, a quality such as discretion, which is having the tact with regard to the truth, or wisdom, which is having the good sense to know that not everything that could be said should be said, or resourcefulness, which is the capacity to make happen what should happen but won't happen unless somebody does something to nudge it along.
David Nyberg. The varnished truth: Truth-telling and deceiving in ordinary life. Citat a Martin Jay. The virtues of mendacity. On lying in politics.