I love the way Elle smiles in the background. Because let’s not forget that Harry was her bully too. She was stuck in a class with him, where he made transphobic comments to her. And not only out of ignorance - it was because “Harry thinks it’s fun to pick on people.” So while Charlie is standing up for himself here, he’s also standing up for her too (and Nick, and Tao, and anyone that Harry has made feel like shit).
“Should I Stay or Should I Go” and “Running Up That Hill” serve the same narrative purpose for both Will and Max. We are clued into Max’s suicidal ideation through song until she’s able to verbally admit that the was experiencing those thoughts in the finale. Will’s song clues us into the same thing, only he doesn’t verbally admit this, he does it through action. Will was constantly trying to contact Joyce from the Upside Down until Lonnie showed up. Once Lonnie, the person who has likely made Will feel worthless, arrived, Will stopped trying.
Billy saying that Max wishes to “follow him” is the same as Lonnie boarding up the wall that Will opened a gate through. Will and Max’s abusers are telling them that they shouldn’t be saved. Will was wondering if the real world was something worth fighting for even though he knew he would die if he stayed in the Upside Down. Will giving up tells us that he isn’t wondering if he should stay or go anymore, he’s made his decision. He’s going to stay in the Upside Down.
They both give themselves to the monster, only to be saved by the love of those around them. El restarts Max’s heart, Joyce and Hopper give Will CPR. They got another chance.
Will’s battle with this doesn’t end there, though. “Should I Stay or Should I Go” plays just before he tells them to close the gate, something that would also kill him. It’s likely that Max will have another moment like this in the next season, but will be saved again.