I'm growing more and more enamored with the idea of Maeglin having borderline personality disorder. Hear me out.
I think that for him it's related to an unstable childhood and early life trauma, like many (but obviously not all) people with BPD. He ends up with an all-consuming fear of abandonment. He has difficulty forming relationships and has that all-or-nothing approach, adoration or detestation. Maeglin latches on to Idril like a drowning man, with all the intense desperation of someone terrified of abandonment and starving for love. Of course he's confused about whether he's romantically attracted to her.
He puts her on an unhealthy and unrealistic pedestal. He idolises Idril, and she recoils from the intensity of it. She rejects him. It's devastating.
He struggles with a lack of social skills. Because of that, he never really finds a place in Gondolin. His inability to form healthy stable bonds only worsens the already crushing feelings of worthlessness. Maeglin doesn't understand his emotional instability, and neither does anyone around him. He lashes out without meaning to. His repressed anger and trauma burst out at the smallest triggers. He becomes self-destructive, impulsive. He's overwhelmed with misery.
So he retreats into his mines in the mountains. He completely isolates himself, all alone where he can't hurt anyone and they can't hurt him.
They don't even notice when he goes missing.
