pronoun, の adjective
A he mister is not just he, it's "mister he," and mister he is your he, your boyfriend.
The readings are the ones you learned with the kanji.
Hey, isn't that Kaoru's boyfriend?
I got this necklace from my boyfriend.
Oh, you got a boyfriend?
You know what, I get in a good mood just from talking to you. You really are my ideal boyfriend.