Ok so i have a theory that Eleven knew she was going to hurt mike. Let me explain, when mike kissed her she didn't smile or be happy (yes i'm aware she might of not known what it meant but anyway) and i was thinking maybe she acted weird because she knew it would hurt him if they liked eachother. Maybe thats why she said she was sorry, because there she had seen she hurts him but couldnt tell him in fear? This is a theory but i really like the idea behind it.