There's a point at one of the pubs where Gary is trying to convince the others that they're having a good time, only for the others to point out that he's over-idolised their youth. While they're absolutely right, and Gary fully deserves the lecture about how he's wrong, the look on his face is very depressing. Made worse when we later find out it's all he has to cling onto.
Shortly after, Gary slips on the urine-soaked bathroom floor, and in frustration is about to punch the wall - when he sees the broken tile of when he broke it back in 1990. He has a startled look that shifts to depression when he realizes he really hasn't escaped the cycle. Even worse, it reminds Gary that his problems did not start after high school, and that he was depressed even back then.
In a climactic fight with Andy, Gary reveals why he wanted to go back to Newton Haven.
After school, Gary's life ultimately went nowhere and his friends have abandoned him since 1997 because of his toxic behavior. At one point, he was committed to a psychiatric ward for self-harming or for attempting suicide (something he never told his family about as his mother still tries to contact him). His time at the hospital only made him feel worse because he felt that they deprived him of his freedom and identity.
Andy: You need help Gary. Gary: I got help. Do you know what help was? Help was a lot of people talking about how fucking awful things have gotten. That is not my idea of a good time. Andy: And this is? Gary: They told me where to go to bed. Me! Andy: Gary. Mate. How can you tell if you're drunk if you're never sober? Gary: I don't want to be sober! It never got better than that night. That was supposed to be the beginning of my life, all that promise and fucking optimism. That feeling like we could take on the whole universe. It was a big lie! Nothing happened!note God help you if you watch this movie first around the time you're graduating. Andy: You don't need to do this Gary. Gary: Yes I do.
After reminiscing about the best years of his life, Gary gets the idea to back to where it all began so he can finally finish The Golden Mile before ending his own life (hoping his childhood friends would forgive him and remember him fondly on the night prior to his death). Except, he's forced to confront how they've all changed and how they are better off without him. By the time he reaches The World's End, Gary has caused the deaths of two of his friends and he's put himself on the front lines of defense against a silent invasion. After trying to sacrifice himself to save Andy, Steven, and Sam: Andy catches up to him at The World's End, just as Gary was about to complete The Golden Mile and finally give himself the closure he always wanted (presumably before he lets the blanks kill him) but Andy prevents him from doing this by knocking the drink out of his hand. Gary is left with tears in his eyes as he begs Andy to "Let me have this!" At this point, Gary's suicide mission for a pint has been rendered moot and he fully realises that he has nothing else left.
Gary then breaks down completely as he admits his depression to Andy, revealing his wounds from self-harming after Andy pulls his sleeves down, explaining how he hates how his life had turned out, and admits how much he envies Andy for having a more perfect life.
In a combination of funny and tragic, when the pair access The Network's base, Gary looks more pissed that he couldn't have his last drink before dying.
This entire backstory is especially tearful once you learn about Simon Pegg's Real Life battle with alcoholism and depression. Just how much of it was Gary and how much was Simon?
Simon Pegg's delivery of "It's all I've got!!" You can see 20 years of depression and anger compressed into that one sentence.
When Andy discovers the wrist bandages, it takes a moment to sink, but he doesn't look at all surprised. And then, instead of asking Gary what he's been doing to himself, he calmly tells him, in his best "closest friend" manner, that he needs help. It's clear that Andy had seen this coming for years. You can also detect a hint of guilt for never trying to prevent it, even after cutting Gary off for one-and-a-half decades.
Unlike its predecessors, Shaun of the Dead or Hot Fuzz, there's no big climatic battle against the Blanks or some dramatic sequel hook. The final fight isn't so much an epic battle against the Network and more a confrontation between 2 lonely men who were forced to talk about how change has affected them.
He never brought any luggage with him, implying he was so unmotivated and depressed that he never bothered to pack. Or worse, he didn't plan on returning home.
When Pete talks about his childhood bully, Gary recites advice from his therapist before quickly changing the subject. Saying "Hey, now listen Pete, bottling up past trauma can lead to inadequate coping strategies in later life... or so I've heard."
Gary's bandaged arms and medical tag are evidence of self-harm and he wore long sleeves to hide this. He also kept his medical tag on so his friends wouldn't blame themselves for his suicide. The fact that he bashes his head on a beam rather than show his arm scars shows that he's also embarrassed by his scars.
There are also no blades in his bathroom at the medical centre and he's grown a stubble, indicating that his razor blades have been confiscated to avoid the risk of him cutting himself.
Gary all but sobbing, "I'm sorry" after Newton-Haven goes up in a mushroom cloud.
"The accident" that ended Andy and Gary's friendship is built up over the course of the film until the smoke house, where it's explained that In 1997, Gary was overdosing, forcing a desperate Andy (who was four times over the alcohol limit) to try to drive him to the hospital, resulting in him rolling the car and almost severing his femoral artery. Gary then somehow recovered enough to flee the scene, leaving Andy alone to be arrested... after the twelve hours of surgery needed to save his life. Andy sees this incident as an act of betrayal because he always believed in Gary.
Even if Gary lying about his mother dying did persuade Andy to join the Musketeers, a deleted part of the script shows Andy saying he only joined because he didn't want another night alone in his empty house. Considering how much Andy wanted nothing to do with Gary after "the accident," that's really saying something.
The reoccurring theme of Gary trying to deal with pain through alcohol comes into play here, In his own manic way, he tries to comfort Pete with shots. He just doesn't properly know how to react to emotions anymore.
For anyone who's a recovering alcoholic or been dry for a long time, this can be rather painfully familiar as a reaction to any heavy emotional trauma.
Pete's beating up Blank!Shane is this as well to an extent. You can see all the rage and pain he experienced finally explode on the now all-but-pacifistic Shane. Then it gets worse because this moment of vengeance costs Pete his life as it allows the Blanks the opportunity to surround him, kill him and create a new Blank from his memories.
Andy initially refuses to join the crawl and is at the point of throwing Gary out of his office, when Gary reveals that his mum died. Watching Gary's face during this scene is heartbreaking enough, but the second time you see the film and you know he's lying it's even worse, because what Gary is REALLY mourning is his lost youth.
Actually, it's worse than that: we learn that Gary's mother has been trying to call him for months, and he's avoiding her, because he doesn't want to talk to her about his suicide attempt.
Made even worse by the ending: after the worldwide EMP sends the world back to the Dark Ages, we learn from Andy that Gary's mother was one of the fatalities. Gary felt bad enough causing the whole thing in the first place, but indirectly killing his own mom? No wonder he chose to walk the Earth.
Doubles as Heartwarming: Gary throwing the keys to the Beast to Steven and Andy before running to The Hole in the Wall. Essentially telling them to run while he stays behind to finish the Golden Mile (and, likely, be killed).
Gary raising his pint in the King's Head to "friends, to Oliver, to Pete," in a very downbeat and bitter fashion.
Sam repeatedly asking about the fate of her brother.
Sam seeing Adrian Keane knowing he died years ago in a crash.
Adrian: Hey Sam, how's life?
The film's use of "So Young" by Suede is this if you see this as Gary deluding himself into thinking he can recapture his lost youth.
When the guys burst into the bathroom to yell at Gary about lying about his mum, Gary is in traumatised tears, panicking about what's happened and pleading with the others not to blame him.
From Andy's tone of voice in the King's Head, when he's trying to get Gary to put the pint down, he seems to have realised that Gary may have a more underlying problem than just wanting to finish the crawl. He starts talking him down, much in the same way you talk someone down from suicide, and on rewatch that can be very chilling. Especially as Gary has tears in his eyes.
Andy: Gary... Put the pint down, yeah?
A more subtle one when Gary follows Sam into the ladies' toilet, thinking she gave him the "sign." She asks him in bewilderment "What happened, Gary?" and Gary first misses completely the point, thinking she is referring to the disabled toilet. But then she asks "No, what happened to you?" and Gary's face expression immediately changes from excited to desolated, while he claims that nothing happened and that he is "the same old Gary." Her response is a concerned, downbeat, "No shit."
While his façade remains pretty much intact until "The Cross Hands," this is one of the few times it slips, probably because Gary didn't expect at all that someone would still be able to see through him, which is also pretty common in depression.
After Gary gave Peter's name to the police officer, Andy angrily asks him "Do you know how much trouble you could get into?" whereupon Gary bitterly answers, "Do you know how much trouble I'm already in?" The first time you watch the movie this short conversation will probably go past you without much effect but when you watch it the second time knowing that he probably refers to his suicide attempt it can truly become tear-jerking, especially since his almost resigned tone indicates that he is perfectly aware of his problems and has already given up, supporting the theory that Gary plans to finally commit suicide after the pub crawl.
Although it's mostly played for laughs in the movie, Gary saying "[...] and knowing in my heart, life would never feel this good again. And you know what? It never did." at the end of the prologue is actually pretty sad.
The moment when Gary puts Sam in her car and tells her to drive away. He tells her that Steven is a better person than him, whereupon she softly answers that he's not a bad person but just not boyfriend material. She's actually right and Gary seems to know that too, and the hurt look on his face when she says that is heartbreaking.
Seeing Steven in The Beast get overwhelmed by an army of Blanks and the giant statue Blank. He tells Andy to leave and while he later turns up fine, Andy's reaction is devastating.
After The Network gives up and emits an enormous EMP that disrupts all technology in the world, it's revealed that most of the Blanks it made have begun to assume the personalities of their templates more thoroughly, essentially resurrecting them. And though several are now heavily mutilated due to Gary and other such survivors having to fight them off, they still try their best to lead their old lives... but in the wake of the EMP, those who found out about the invasion have developed a belated hatred of the Blanks, meaning that an entire group of people now have to evade destruction at the hands of people who want them dead for things they had zero control over.
Despite all the insistence that the Blanks are not slaves... yes, they were under the Network.