After season two, Mike started to spend a lot more time with Eleven when they started dating. Of course, this is a normal thing to do, but I'm sure most of us have had that one friend who ditches us for their significant other, right?
With a mixture of Will struggling after returning from The Upside Down, and Mike dealing with new feelings, it's easy to see why they started to grow apart. Fans criticised Mike's reaction to Will coming out in season four, even Finn Wolfhard who plays Mike said, "He's just such an idiot. I don't understand. He's very very very clueless. Yeah, it was pretty heartbreaking to actually do that scene… I was just like how do you not understand that your friend is struggling through something?"