Confidant -

Confidant (noun)

[kon-fi-dant] / ˈkɒn fɪ dɑnt/

Meaning: a person with whom you can share secrets or private matters and trust that they will not tell anyone.

We all have some people in our lives with whom we can share all our secrets, and share anything with them. And, we know for sure that they will not tell anyone. It can be a friend, a sister, a brother. Such people are called Confidants. The act of putting your trust in them is called “to confide“.
I confide in my brother. He is my confidant.

Imagine, you have a close friend named Andy. You both work in the same office. You have a crush on the office receptionist Pamela. Andy is the only person in the office who knows about your crush. You have 100% confidence that Andy will not tell anyone.
In this situation, You are confiding in Andy and Andy is your Confidant.

Other forms of Confidant:

Confided, Confiding, Confides (verb)
Confiding in her was the biggest mistake of my life.

More examples using Confidant/Confide:

I failed one subject at school, but my parents don’t know about it. Only my brother knows about it and he is my trusted confidant.
The car driver was the minister’s confidant.
Julie’s brother is her confidant. They have no secrets between them.
I felt like I can confide in her, so I told her everything.
John was a close friend and confidant of Diane.