Do you ever think about how in 2x04 Will was absent and didn't pick up the phone for one day and he immediately assumed he was in danger and Mike was sad and lonely the entire day and could only think or talk about Will -
And how he went to Will's house as soon as he could after school?
And how Will didn't pick up for 6 months - but this time he was across the country?
"Anger is just sadness that had nowhere to go for a very long time"
We saw how Mike was with Will after missing him for just a day. I think if Will hadn't picked up for a week, a month, he would've hugged him that much tighter. But Will didn't pick up for 6. And by then he couldn't hug him at all.
These are the same scenes. The first gif happened. You can be sure of it. But this time, it passed. This time, the sadness didn't have anywhere to go.
One thing Mike does is he never asks if Will knew he tried to call. Or tried to call back. That's why he's so surprised when Will says "what about us?" When Will cares at all. He felt like he was yelling at a wall. Someone who had been a wall all day. Someone who had been a wall all year. Then that someone said "I care about this relationship and I didn't get your calls". The fight isn't Mike talking to Will. It's everything Mike wanted to say for 6 months of no calls too, just like Will.
If Will had called him back in November, they would have talked all night. But he didn't hear from him until March. March 22. And we see what he's become from it plain as day on March 21.