once again, i'd like to point out that stranger things is a tv show. the characters are not real. why is this important? all scenes and narratives are written a specific way, they don't just happen by themselves. for example, this means:
in 1x03, the writers chose to emphasize mike's reaction to will's "body" being found in comparison to lucas and dustin's reactions. they easily could've shown all three of the boys' reactions, but instead mike was the focus and got multiple scenes of his shock and anger over will's "body" being found.
in 1x04, the writers chose to focus on mike being depressed over will's death. they didn't do this for dustin or lucas, even though all four of the boys are introduced as a group at the beginning of the season.
in 1x04, the writers chose to have mike shove troy in the gym for making homophobic comments about will. any one of the boys could've taken offense to that, but instead, mike is the focus while lucas and dustin stand off to the side.
in 1x04, the writers chose mike to be the one who recognized will's voice over the radio. they could've easily had the entire party there for that scene, but instead it was just mike who immediately knew will's voice.
in 2x01, the writers chose mike as the one to follow will out of the arcade and bring him back inside. it could've been any of the party members, but instead mike was singled out as having noticed will disappeared.
in 2x02, the writers chose to have mike be the one to comfort will after his "episode," even though the whole party is trick-or-treating together. it could've easily been written as group bonding where will tells everyone about his visions, but instead the writers gave us the crazy together scene.
in 2x03, the writers chose to focus on mike at school when will is acting weird. it was specifically chosen that mike was the only one to notice will was "quiet today" and that it was weird he missed class, while the rest of the party didn't notice anything was wrong.
in 2x08, the writers chose to have mike be in the shed with the rest of will's family. there could've been a cute scene of the whole party trying to reach will with stories of their dnd campaigns, but instead mike is the only non-family member present (not counting hopper because he didn't share any memories).
in 3x01, the writers chose to make the movie theater full enough that mike/will and lucas/max couldn't all sit together. this was directly after lucas implied going to the movies was the equivalent of "spending romantic time" together.
in 3x03, the writers chose to have mike and will get into an argument at the wheeler's house, even though lucas was also there. lucas didn't just happen to stay behind in the basement. it was a clear choice that mike and will got into a fight, just the two of them.
in 3x08, the writers chose to give will and mike an individual goodbye scene, even though the only other individual scenes were jancy and mlvn (two couples). there could've been a scene of the whole party saying goodbye but instead the writers specifically had a (flirty) goodbye scene between mike and will, directly contrasting the (extremely) awkward mlvn goodbye.
in 4x09, the writers chose to give mike and will another heart-to-heart in hopper's cabin right at the end of the season. will could've easily told everyone there that he still knows vecna is alive (this is probably what should've happened honestly), but instead only told mike-- when el was right there! the clear choice to give them a special talk right at the end of the season was very telling.