A bosom friend is good to you, unconditionally; A confidant is sincere to you and will not cheat; A bosom friend is good to you and has no purpose; A confidant hurts you, not to take it.
Knowing yourself is a very subtle relationship, between love and friendship, then lovers, and then strangers.
A bosom friend is when you are in trouble, you can get it off your chest with him, and another person will become your listener. When you are at a loss, you can communicate with him to seek answers and solve mysteries, which can make your mood suddenly clear. When you encounter difficulties, you can get his encouragement and enhance your motivation to move forward in life.