Nathan's mother kicking him out of the house in the very first episode. He's rude, sure, but coming home only to find out his mother changed the locks with no warning and won't let him in at all is fairly heartbreaking. Especially when he starts calling people to try and find somewhere to sleep, becoming visibly disheartened when everyone turns him down, and ends up on a mattress on the community center floor for lack of anywhere else. And all of this is because his mother just wants her current boyfriend to work out because the previous ones couldn't stand Nathan. Even if he is a prick, it's hard not to feel bad for him being so unceremoniously kicked out.
Simon's whole superpower. The poor guy is so alone, so isolated, that he literally becomes invisible. Most evident in its first scene, where he's begging someone, anyone, to listen to him. And thats before the invisibility sets in.
Episode 2 sees Nathan attract the attention of a beautiful young woman, only to find out that she is actually 82 and the storm de-aged her. She, however, is rapidly turning back to her own age, and the results, suffice to say, do not end well for anyone concerned...
Probably the most poignant moment, beyond their second meeting at the second OAP's night, is the very end of the storyline, where Nathan goes over to her house, presumably to apologise, and finds her dead in her chair, an open album in her lap showing her as a young woman. Nathan, in an uncharacteristic moment of kindness, kisses her forehead as he leaves.
In episode 4, we get to see how each of the characters was spending their time before episode 1, including Tony and Sally. Kelly and her boyfriend steal Tony's car, and Kelly's boyfriend proposes to her with a ring he finds in the glove compartment, leading her to proclaim "that is so fuckin' romantic". We cut back to Tony, who goes manic. He admits to Sally he was going to propose to her, to which she replies "Can I still say yes?" It's just heartbreaking, knowing what'll happen to them.
Nathan's first death.
To add to that, Kelly's reaction to his death is quite sad, starting from her screams after he's been impaled. During his funeral, Kelly, who only met him weeks ago, is the first to arrive to the church, and places his phone in the coffin before taking a seat in the pews, sombre and in black. She's the last to leave his grave as well, after Alisha says they should all go out for a drink, and heads off early. When Simon give her the video he made about Nathan, she cries watching it. It's sort of simultaneously heartwarming, considering Nathan didn't have any real friends apart from her, and tearjerking.
The scene in the final episode where Simon hides in the freezer room. Every episode of the first season shows him getting more and more isolated (even down to how the camera films him), with Sally luring him in and betraying him being what sends him over the edge. How much more absolutely isolated can someone be than sitting alone in a small, freezing metal room, munching on a slice of pizza and staring in paranoia out the window, with a corpse propped up as if for company? It really shows how badly things might have gone if the others hadn't been there for him.
In the original scripts and storyboards, Simon was going to turn into a villain in the last episode, as a final product of his isolation. Once you know that, these scenes get even worse, as you can see his steady slip towards another mental breakdown. Even worse on rewatch, once you get to know him as a hero, and you see that he has so much potential just waiting to be unlocked.
Nathan in the Alternate Universe when Curtis doesn't save them from Tony. He's so, so different and it's incredibly jarring, and heartbreaking when you think of the survivor's guilt he must be going through to evoke such a dramatic change.
He's still got stitches across his forehead, indicating it hasn't been so long since the incident. It's compounded by the tributes that have been left at the door for the five people who died, including Gary, indicating how many people were affected by their deaths.
Simon starting to have a mini-breakdown after he's discovered with Sally's body, as he fears being rejected by the group he feels closest too.
His reunion with his dad at the end, as well as his dad's reasoning:
Nathan's Dad: I thought I had to choose, and I chose you and your mum. And I haven't been a father to either of you.
Nathan's bitterness over his 8th birthday; it's worth noting he only tells Jamie about it because he doesn't want him to think their dad's rejected him any more than he rejected his normal family. In the same scene, he admits he probably wasn't a very easy kid to raise. Throughout the whole episode, Nathan seems genuinely happy to have a brother, in contrast to his usual attention-seeking behaviour, and looks out for Jamie in more than one way. it makes it even sadder how things turn out.
Superhoodie dying in Alisha's arms, while she cries that she loves him, and future!Simon tells her it's all going to be ok.
Superhoodie It's you falling in love with him that makes him become me.
Alisha staring after Simon, feeling absolutely distraught, not being able to tell him that it's because she knows how he dies.
Superhoodie/Simon's death, and him asking Alisha to burn his body because no one can know that it was him who saved them. She loves him so much, and knows that the current Simon isn't him yet. Then she goes to his lair and finds the photo of them in Las Vegas- the city she's always wanted to visit.
Bruno's confession to Kelly
Bruno "Do you understand now? I just wanted to be human. It was all worth it, to be with you.
The scene where Simon finds Nathan, or what remains of him and both Simon and the audience see, really for the first time, that immortal doesn't mean invincible.
Rudytoo admitting his feelings for Alicia. And, despite his insistence that Rudytoo is lying and he doesn't care about her, Rudy still sacrificed himself to save Alicia.
Rudytoo being rejected by Rudy, who is basically like his twin brother... only closer.
The look on Simon's face when he wakes up from his Freak Out!, sees Alisha, and realizes he broke up with her under Peter the Fanboy's influence. Puppy-Dog Eyes in the most stricken and horrified expression. First he freaks out as it appears his reality is literally being torn around him, then as soon he sees Alisha he begs her to forgive him with the most desperate reaction you can imagine. Thank God she does.
Friedrich's letter explaining his attempt to assassinate Hitler, and his plea with Seth to fix history.
Friedrich's and Curtis' deaths in the Nazi timeline.
The death of their probation worker Shaun. After all, he is the probation worker we've got to know best.
Having "This Is Not The End" by Clare Maguire playing makes it so much worse.
His line about not understanding why Kelly killed him is also heartbreaking. Even though he could be a bit of an apathetic ass at times, he really wasn't a bad guy, and he seems genuinely hurt that one of them would just walk up and stab him like that. The others seem to agree - they wouldn't let him die thinking Kelly killed him and told him everything.
Alisha's death, especailly as we all thought she was safe after being attacked by Sally's ghost. The look in Simon's eyes makes it so much more heartbreaking.
And then knowing exactly how Simon and Alisha's time loop will play out. Destined to love and lose each other in a never ending cycle. Tear Jerker doesn't even cover it...
Watch S3 E8 and then go back and watch S2 E3, knowing how far that Future!Simon come to be with Alisha, knowing that he's just recovered from watching Alisha die, knowing they both will die, knowing Simon knows he's about to die, makes all of their interactions, especially on Simon's behalf in S2 E3 so heart-breaking it's extremely hard to watch. It's pure torture.
Much of episode 3. Jess gets a "Reason You Suck" Speech from Third Rudy, then gets her romantic hopes with Alex crushed, and breaksdown when Third Rudy stalks her, temporarily discarding all her defences and dignity.
It then gets worse when she tells Third Rudy about how several years ago she had an eating disorder, was supported by a close friend who then abandoned her after she slept with him (a pattern that this scumbag repeated with other girls), so she then tried to commit suicide with pills and vodka.
Jess telling Third Rudy how killing someone is "horrible".
Rudy and Curtis's phone conversation right before Zombie!Curtis commits suicide. Rudy pleads with him to come up with a way to fix this, and then to come for a pint so that they can say goodbye properly.
Curtis: There are no happy endings.
Just Rudy's face during the entire part of that episode.
Finn persuading his half-sister Grace to let their dying father go, rather than use her power to preserve him in pain. She breaks down and almost kills him when he tries to stop her, but he calmly tells her that she can't, as he's family. Finn just promises that she can let their dad go, as now she has him to look after her.
Alex placing a gun to his head when he thinks that he can't get his penis back, stating that he can't go on being a mocked freak who hates himself.
While it's not given focus, the brief glimpse we get of the trans man who originally stole it tells us he knows exactly how Alex feels, having born into that same situation.
Rudy telling Nadine that he understands why she's remaining a nun rather than being with him: compared to the son of God, he's "just a dickhead with a big mouth". He then tells a statue of Jesus to "be nice to her, she's special".
Nadine sacrificing herself to stop the Four Cyclists of the Apocalypse, telling Rudy that she loves him and is glad she met him, and thanking the Misfits for offering to sacrifice themselves for her.
Rudy Too letting out all his various worries and inadequacies at the storm meetings.
Abby breaking down in tears because she's been rejected by Laura, her lover and creator
When Finn has his will to live stolen from him, and Alex grabs him when he tries to hang himself, Finn pleads with Alex to just let him die.
Mark being killed, and Abby's shocked reaction.
The tearful reaction of Rudy to Jess reappearing after a year.