لِي مِنْ فُلَانٍ صَدِيقٌ حَمِيمٌ
I have, drawn from so-and-so, a deeply devoted friend.
The point is not that the man introduces a separate friend. The man himself is so loyal that the expression imagines another intimate friend being extracted from his person.
Min precedes the source “fulān,” while “ṣadīq ḥamīm” is the extracted figure. The shared characteristic is the depth of friendship.
A direct sentence such as “So-and-so is an intimate friend” asserts the quality; the extractive construction adds an image of its abundance or perfection.