Nancy found him there, tear stained, curled up in a ball, clutching a walkie talkie.
"Mike? Mike, wake up."
"Nancy?" He said sleepily
"Mike, it's twelve thirty, what are you doing in yesterday's clothes?"
He nodded towards the bathroom
She walked in, horrified to find a bloodstained sink and a broken mirror
"Mike, what did that?"
"Me, I am the monster."
After a long pause he explained
"Will knew that El was in the upside down, calling for me, ever since he got back, he knew, he said that dead people don't come back to life, he's a perfect example that they do."
"So why is there blood in the sink?"
"I punched him."
He felt that his actions were justified, but he felt disgusted with himself, this isn't the person that El left, this isn't Mike, this is someone else.
Nancy didn't know what to do, he had punched his friend in the face, but that same friend treated him like he as crazy, when he knew he wasn't.
"Mike, go get some sleep, in your own bed."
"Ok."
He got up, and went to his room
He didn't feel like he was in control, he felt as if his impulses were more powerful than his control over them.
His dreams didn't improve, now instead of feeling of losing her again, he felt the guilt, of knowing where she is, but not being able to get to her. If Will was right, and she was in the upside down, there was no way he knew of that would get him there. After Joyce and Hopper got back with Will, the gate closed behind them, there was no gate into the upside down anymore, and she was in there.
The next day was a sad one, instead of anger, Mike only felt sadness. When he got to school, he got a glance of Will, his face looked better, he also got a glance of Troy, his face didn't. He got a familiar pain in his heart, he saw what he had done, he didn't have control of the thing that did this, he didn't know what did it in the first place.
School felt lonely when he couldn't make eye contact with his friends without a reminder of what it had done, what he had done. The painful guilt, that he had hurt his friend, one that trusted him, but Mike had trusted him, and he betrayed it. He spent most of school trying to figure out how to get to the upside down, his only plan involved Will, and he didn't think he could ask him to do what he needed, even though he was mad at him, he was still his friend.
That was the question, How much was he willing to give to get her back?