What Mike means:
I can't stop worrying about Eleven because she's so reckless and gets herself into danger all the time, but like, why do I care so much anyway, because it's not like I *like* her, she's just so cute and kind to everyone, but I definitely don't *like* her...right?
I love the image of Eleven seeing her first Christmas tree and being so enchanted and Mike of course being enchanted by HER like the lovesick kid he is. EVEN BETTER, they turn off all the lights in the living room except for the tree lights and both of them just lie down on the floor and look up at the tree, amazed by the way the tiny lights cast their glow around the whole room.
They would’ve spent her first Christmas together. He would’ve showed her all the wonder and joy and warmth that is the holidays. They would’ve obliterated the other boys in a snowball fight and struggled to wrap presents together and, if he was brave, kissed under the mistletoe. He would’ve taken her into town to show her all the decorations and lights in the storefronts and seen how her eyes light up in excitement at the falling snow. He would’ve spent the whole month making the perfect present for her, and he would’ve always made sure she was wearing mittens so her fingers wouldn’t be freezing. Instead, he will go along with the Christmas shopping and the visiting relatives and the obnoxious amount of lights that his dad puts up, and he will never truly be home. She is his home, always will be. The trust in her eyes when she looked at him, the innocent happiness in her smile when she laughed, the strength he felt when she held his hand—now, only worn fragments of memory. On Christmas Eve, he will wrap her present and bury it in the drawer beside the sweatshirt and sweatpants, dreaming for a moment that…he was home for Christmas