I’m thinking they both have ptsd. Something happened in that room, and the childhood friend now wants the MC to open the door.
With ptsd, it’s a lot of “fight or flight” instincts. People going through trauma will either lash out, hide, or unconsciously seek that trauma.
If you notice, abusers tend to be victims of abuse themselves. “My father hit me too” etc etc.
They both share a common trauma, the MC is hallucinating and trying to cope. He even FORGOT the source of trauma, while the childhood friend grew up remembering everything.
The childhood friend gives off a cold kinda scary feel while the main character is being strung along by these new waves of emotions, the childhood friend, and having to keep up with his everyday stuff.
Anxiety disorders like this tend to take a toll mentally and physically. Trying to cope with unknown feelings and not being able to control your emotions makes everything worse.
I think the Mc has antisocial disorder, or something close to that. It’s definitive that the Mc doesn’t care about others except that one dude (I’m bad at remembering names). The mirror represents his actual mind, and he’s having all of these psychotic ticks going off because he’s been living the life of a lie. He’s acting like a normal person, when in fact he knows he’s different. He will hurt and kill others to benefit himself. He will step over people without a care, except this time, he wants his childhood friend. My theory is that both of them have antisocial disorder (or something close), and they can relate to each other so they feel the need to have (?) each other. No sane person would get mad enough to put out a cig on a forehead. And the reason why the other guy has it (his friend) is when you can tell he has clinical intentions, but switches to a nice person when he wants something (like chatting with his publisher in the cafe).