Now, this is subtle, but it is shown in season 3 too where Lucas says; “Oh El, I wish we could make out forever and never hang out with any of our friends”. No shade towards Lucas at all, but, I do feel like Mike was trying to be like him in some way (their outfits are the same too), especially in this scene where he says; "If you love her so much, why don't you marry her?" This is also another form of heternormativity in the 80s, causing Mike to feel like he is supposed to like girls. 

This is a very obvious one and I feel like Karen is suspecting Mike liking Will even before he knows, which is kind of funny. She says; “All this that’s been going on with Will, I can’t imagine what it’s been like for you. I just … I want you to feel like you can talk to me. I never want you to feel like you have to HIDE anything from me. I’m here for you okay?” Mike seems a little confused and nods his head slightly before going back upstairs to El who is in his CLOSET. 

This isn't that much Byler evidence, however, when Troy and James are mocking Will's 'death' and call him homophobic names, this is the second time that it has happened. The first was after the scene above and for some reason, Mike is the only one specifically targeted in both when they joke about Will being gay. Then afterwards, Mike defends Will by pushing Troy over in front of the whole school.

Mike's main and only focus in season 1 is to find Will. This really contradicts his monologue in season 4 which we will dive into later. He refers to El as a WEAPON and wants to 'get rid of her' so that they can continue looking for Will. Yet, El says no to this (rightfully so) and stays in his house. When he learns that bad men are after her, and that he himself might die, he realises that if he is dead then he is no use to Will.

When Will's fake body is pulled out of the water, Mike spirals. He blames El and says; “Mike? Mike what?! You were supposed to help us find him alive! Why did you lie to us?! You said he was alive! What’s wrong with you?! What is wrong with you?!” Once again, saving Will is his main priority above everything else, and he is now back to treating El like she is just a tool to find Will. 

A screenwriter explained that a big way to establish a character is to have them make a choice. The first major independent choice Will makes is to defy Dustin and Lucas and tell Mike the truth during their DnD campaign at the beginning of the season. The first major independent choice Mike makes is to defy Hopper and look for Will. The writers wanted to show how Will and Mike love each other. 

Mike was the only member of the party that recognised Will's crying/whimpering; “Does that sound like a baby to you? That was Will." The others, Lucas mainly, don't believe him. I think this scene shows how much Mike loves Will to recognise only a few noises he makes. Especially since the only other person who recognised Will was his mother. 

Mike is upset at the dinner table when Nancy (sort of) blames Will for not being able to hang out with Steve, which then causes Nancy to storm off. Ted proclaims; "See Michael? You see what happens?" which I'm pretty sure what he means is that this is what happens when he shows a lot of care for his male best friend. Mike doesn't pick up on the hint, however, and yells back; "What happens when what?! “I’m the only one acting normal here! I’m the only one who cares about Will!”

Because El looks like a boy, as stated by many others in the show, it gives Mike an opportunity to project his feelings for Will (or for boys in general) onto El. Troy says; "She doesn't even look like a girl." Benny says; "You think you can steal from me, boy?" and Benny's friend says; "At lunch, there was this boy..." This may be a reach, yet I still think its important to note. El even gets mistaken as Will at one point by Hopper.

Once again, keeping El safe isn't the most important thing on Mike's agenda. Although throughout the series he develops a strong sense of care for her, here, he doesn't. He only wants Will back, which is his first and upmost priority. Mike says; "El can find them." even though she is clearly exhausted and needs rest. Lucas and Dustin seem to understand this, but Mike is desperate for his best friend back.

When Lucas and Dustin were both asleep, Mike stayed awake so he can be the first to see Will when he wakes up. I just find it extra cute that he was successful in this endeavour with Lucas and Dustin hugging Will at the same time and Mike, being so fast, got to hug Will on his own, specifically putting his head onto his heartbeat.