Nature’s Worst Miracle

Mairon was bound to fall and to worship Melkor. He had known Eru in his measure and yet, when he and Melkor were together, he felt closer to divinity that he ever had before. The emotions he was experiencing felt natural and good despite leading him to 'sin'. Thus it didn't take him long to be freed from any sense of guilt, and thereafter he was unable to repent in a genuine manner for what he felt. His fate was sealed since the moment Melkor laid eyes on him.

I love the idea of Mairon being king over Angband even in the first age, he is the king, the people answer to him, not to Melkor, and this isn´t because Melkor is less powerful, but because Melkor is so much more powerful. Melkor is the god! It is unfathomable to go to him for governance matters, hence, Mairon is king over Angband, and Melkor is god over Arda.