confident, confidant

Confident or confident means self-assured; having a strong belief in one's abilities or the outcome of a course of action--
He was confident that he would pass the test.
He is socially confident, and enjoys meeting new people.

Confidant or confidant ( sometimes spelled confidante when used to mean a female ) is a friend to whom one would tell one's secrets--
Her sister was a close friend and confidant, always ready to listen.
She trusted her confidant with all of her secrets.

Now that you know that, you can say--
"He was quite confident that his confidant was trustworthy."

Note--"confidence" may mean the feeling of being self-assured or sure of an outcome--
His employer had confidence in the young man's abilities.
"Confidence" also means a secret, or a relationship of trust--
He took his associate into his confidence.
She would never betray a confidence.
Note # 2--a "confidence man" is a con artist--someone who perpetrates fraud or financial schemes on individuals by gaining their trust--
When he told the woman he had found some money, she knew that he was a confidence man.
Not to be confused with a "confidente", an old-fashioned type of settee or sofa. The plural ( more than one ) is "confidentes"--
They bid on two old confidentes at the antique auction.
"Confidants" or "confidantes" would be the plural form of "confidant" or "confidante"--
They were lifelong confidants.