A person kissing themselves in the mirror is something I've seen many many times in films and music videos, but never knew what it meant. That photo of Jonghyun reminded me of the movie "Neon Demon" which I gotta say is the most illuminati film I've ever seen.
In one part the main character (Dakota Fanning) ends up kissing her reflection in a pyramidal pair of mirrors.
I couldn't find a video but here is a picture of the scene I'm referring to:
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The movie talks about the story of this very yong girl (underage) that wants to become a model and moves to Los Angeles to pursue her dream. It is a very disturbing story with a lot of symbolism and heavy themes like p***philia, murder, canibalism, lesbianism, and of course satanism.
In that part of the film (from the picture above that reminded me of Jonghyun) she is in a fashion show, she became the muse of a famous fashion designer (aka he is her handler now) and while in the runway you can see she looks possesed, transformed, like she is not herself anymore. Very ritualistic and full with symbolism. The acting is very poor in the film but its still very interesting if you guys want to watch it, it gives out very interesting insights on how things works.
Anyway, going back to the kissing part. I think you are right, it does seem to depict a ritual of some sort, a sexual ritual. I think that in these rituals you are forced to perform gay acts with others, so maybe that is why these artists are kissing themselves with a sexual demeanor, maybe representing the acts they do with the same sex. What I mean can be seen in the movie "Eyes Wide Shut" by Stanley Kubrick.
This is what I mean by representing the sexual rituals with same sex people:
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In the film, the women in masks are almost completely naked (humiliation ritual) and go in a circle kissing one another on the lips, infront of everyone. Maybe the kisses from before represent that magick ritual?
Or, like you said, it could also represent the fragmentation of the self. Usually these people have alters that are very sexual in nature, almost like animals, and these alters can be brought up by the handlers, working them as sex slaves. A mirror usually means the fragmentation of the self.