So this takes place after the nematon but Derek never left.
Derek silently cursed himself as he sat in his Camaro staring at the graveyard. He should get out of the car. He should join his former pack in mourning. He should cry. He should tell them how he had the chance to save Stiles's life but was too stupid to realize what was happening. But he won't do any of those things. He resigned to sitting in his car, hating himself for giving up on the one person who deserved so much more than Derek was able to give.
Everyone who knew Stiles had showed up for the funeral. The cause of death was known all over town. When the sheriff's only son kills himself, everyone is going to know about it. What no one knew was why. People speculated, of course, but only a couple knew how bad things had gotten for Stiles.
Scott had watched Stiles withdraw from the pack. He knew something was off about Stiles for the past month but Stiles refused to talk about it. Scott eventually let Stiles pull away. He didn't know what else to do. He tried for weeks to be there for Stiles but in the end, it seemed that the more Scott tried, the more Stiles shut down. Scott knew he would blame himself for the rest of his life.
Lydia didn't know how to help Stiles. She had a sense that there was no saving him. Stiles's condition over the past month made Lydia hate being a banshee. She always felt scared for him whenever she was around him. She could tell he was locked in his own head. She could tell he wasn't really there anymore. Stiles was dead and Lydia couldn't figure out why she couldn't help him.
Allison felt selfish. She hadn't paid attention to Stiles lately. She was so freaked out about the darkness around her own heart that she didn't even think that Stiles wasn't able to cope with what the nematon did to him. She knew she held some of the blame.
Isaac wanted to scream. He wanted to wolf out and just run through the woods for days until he was so far away from all the tragedy Beacon Hills had always seemed to hold. He was going to intervene with Stiles soon. He saw how hollow and dark Stiles had become and it was making Isaac sick to have to watch Stiles pull away from everyone. He hated that he was too late. He knew he had a part in Stiles's death.
Sheriff John Stillinski stared at the hole in the ground that was now his son's home. He hadn't seen it coming. He felt like a horrible father. He'd been too worried about saving his job and helping out the town that he didn't even make time to save his own son. John knew he would never recover from this. He didn't really want to. His entire family was gone and there really was no point to pretend that he could be normal again. The only thing that had kept him from following in his son's footsteps was the note he found on Stiles's bed after his body was taken from the bedroom. John would live out the rest of his life in misery with the help of alcohol and work.