Just detached from reality real quick and when I came to, I had this in my notes (aka this song is so Willleno coded in my eyes): Will didn't text Leno on his 21st birthday because he was too scared that Leno would leave him on read or he would find out Leno blocked him. The worst part is that he would deserve it for breaking Leno's heart - the heart of the boy he grew up with but couldn't keep to grow old with.
So instead he calls Gabe - loyal, soft and forgiving Gabe - with the excuse that he was bored, when in reality the thought of him missing Lenos 21st birthday makes him feel lonely and miss the times at bc when everything felt easier and he wasn't just in the shadows of someone but rather the boy in the spotlight. On the call with Gabe, he can't help it and asks about Leno's birthday, to which Gabe says that it was miserable. Maybe Leno can play it cool in front of everyone else but not in front of Gabe because Gabe knew. Gabe had offered to be by Leno's side ever since Will left. But Leno didn't let him into his heart enough to see the gaping hole Will left there. Still, Gabe knew it was there because he knew Leno, and he knew that the spark in his eye went away the day Will left.
So of course Gabe confronts Will for not texting Leno, to which Will mumbles with his voice laced with sadness: "You know he doesn't wanna hear shit from me," and Gabe responses with soft honesty in his voice: "Can you blame him?"
And no, Will can't blame him because it's on him. He left, he broke the promise of another year at bc and he didn't even text his once best friend on his 21st birthday.