bosom friends 知心朋友

A：Is Jack a friend of yours?
B：Yes. He is one of my bosom friends.
A：He’s a nice guy as far as I know
B：You can be certain of that.

甲：杰克是你的朋友吗？
乙：是，他是我的一个知心朋友。
甲：我也知道他是一个好人。