He remembers the way her eyes looked as she left. The brown had dulled in a way he had never seen, she seemed so unfamiliar to him in those last minutes. She knew something he didn't, and he was too much of a coward to pry it out of her. After everything he left her with a glare and turned his back to her. It swallowed up his heart but it was the only thing he knew how to do in that moment, he only knew how to walk away because that, confronting that would have killed him. It was as if every memory they made together faded with the tires of Hoppers car taking her away, they were replaced with a dark haze. He didn't know how to sympathize with her, she choose to leave instead of fighting this with him; with everyone. He was there when she first left that hell hole and he was there for a whole year as she was in the dark and he was there when she came out because he loved her.
He loved her and she left.
Mike didn't leave the room for 2 days after she was gone. Nancy tried to come in, she told him she knew he loved her and it has to hurt him, he is just a sixteen year old boy and that must have burned his little soul, but he looked at her, really looked at his sister and told her " I don't feel anything Nancy. Since the minute she left i've felt nothing." She watched in horror as his eyes looked into her, empty as if he was a ghost of her brother. She blinked and tried to gather something to say,but the way he looked, she was too scared to say a word. She felt as if anything now would set him on fire and she did not want to watch Mike burn. She knew what he was feeling, he knew El was probably going to die, she walked away on a mission that for the last time would save the world but set his ablaze. He knew she wasn't coming out of this one, she was going to either die or he would never see her again. Mike Wheeler was rotting from the inside out. In his dreams that night, he saw her, bloody nose, eyes frantic, he watched as her red lips parted, screaming so loud it burst the blackness of where her bare foot stood and she fell into nothing. He watched as the shadow monster devoured her, and he listened as she begged for him. Mike woke up screaming that night, empty, and full of hate.