guys my brain ain’t strong enough for this, can someone explain the ending to me?

Same.

Man same

Both switched with their mirror selves for sometime ago. Everything is served in subtle context as far as I can see. But from last chapter you can see their personalities from childhood is opposite of how they are now(fears and reactions) . And black hair doesn't have any memory after the incident. It seems now they completely became their reflections.

The reflections said that the real bodies and their reflections are actually one and if they deny the reflection they are incomplete. So I guess they have fused with the reflections and let their malice to cut lose. Also joon chose to forget but know he remembered everything