Even before the accident, Andy and his posse are the best of friends. They've been in school together for years, have each other's backs, and know how to have a good time. In the brief time they have together before the accident, we see them joking around, talking about girls, and laughing a lot—you know, how friends do.
But these guys go through a traumatic experience together that none of them will ever forget. The accident doesn't just change Andy, but each of his friends as well. They all experience some form of guilt over what happened that night, whether it was their fault or not. The only problem is that instead of dealing with the death of their buddy together, Andy separates from the pack—he no longer hangs out with his friends anymore, which makes him feel worse. His friends, however, stick with each other. Or, the ones who remain do, anyway.
Andy's friends tell the coach that he's been pushing them away ever since the night of the accident. They complain, "He's been real moody lately, Coach. Sometimes he just likes to be alone. He don't talk to us like he used to" (10.4). Andy might feel like no one cares about him when he commits suicide, but in reality, he isolates himself from his closest friends. They're there for him the entire time.
It's clear that the guys really care about Andy and want to get him the help that he needs—they don't stop with seeking help from their coach, and even go to see the school counselor (whom they don't like). She doesn't do much to help (okay, she totally brushes them off), but she does tells the boys they're "such good friends" (24.35). And while she's wrong about Andy being fine, she's totally right in her assessment of these guys.
When Andy commits suicide, it doesn't just affect him—it leaves his friends feeling hurt and alone. As B.J. says, "Andy left without sayin' good-bye and I don't know why. He had friends that cared about him that he didn't ask for help. I feel like he punched me in the gut and I can't hit back" (43.14). It's not just about Andy anymore, then, his death is also about his friends. They don't get why Andy didn't turn to them for help if he needed it. That's what friends do, after all, and they all would have been there for him.
Instead, Andy leaves his group of buddies down yet another friend. Poor guys.