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。
乙:这点毫无疑问。