Mike is a character that needs a lot of grace. Will is a character that gives a lot of grace. That's why Byler works. Only Will understands that Mike makes honest mistakes and is still willing to give him the chance to make things right. Why else is Will so ready to listen to Mike when he's pleading with Will to take him back again in s4?
Will never holds Mike's imperfections against him.
Ok so you know that byler theory that in the movie scene in s3 Mike grabbed wills hand and THATS why he kept looking down? Well what if I add on to that and say that the hand he grabbed is the same one he held in s2 that broke Will out of possession for a while to use morse code (in the s3 scene he’s also having visions and only breaks out of them when Mike holds his hand)?
Omg in case we do get to see Kali again in s5 im actually really curious to know what a friendship between her and Will would look like because she’s the one that was able to bring els powers to another level in s2 so rather that upgrading powers would she bring them out in Will?
s5 Mike having a breakdown and needing a hug. Will initiating the hug instead of Mike, and Mike collapsing tiredly into Will's arms. Will remembering s2 Mike's words towards Dustin on Halloween - where Mike said "I got him. I got him"
So Will borrows that, but instead switches it to "I got you. Mike. I got you."