This is based on opinion. Please don't list it on a work's trope example list.
Tearjerker / Orphan Black
Sarah crying because she thought Kira thought she was dead.
"No, Fee, no, oh god, Fee, they can't think I'm dead Fe, Kira can't think I'm dead!"
When Sarah goes to the neolutionist club to rescue Paul, Felix tells her to try not to die. He tries to lighten the mood with his usual witty one-liners, but its painfully clear that he's terrified for her.
Then in the next episode, she bursts into tears at the hospital.
Kira: Helena? What happened to you?
Helena: I don't know...
Helena's gut-wrenching reaction to seeing Kira hit by a car. She looks more horrified than Sarah.
It's hard to watch Tomas put Helena in a cage. Given the nature of their relationship, it comes across like child abuse (even though Helena's an adult).
Watching Alison's "perfect" life spiral out of control until her friends and family host an intervention. While it starts off cheesy, it gradually gets more emotional, until Alison leaves crying because she can't tell them what's really going on.
Cosima finding out that Delphine was a neolutionist.
Delphine desperately trying to convince Cosima that she really does love her, she is genuinely trying to keep her safe and she would never put Sarah's child in danger. It sounds too good to be true, Delphine's heartfelt assurance are exactly what she wants to hear, and she cannot take the risk. The audience knows that every word is true. Cosima doesn't.
Delphine stoically accepts any and all accusations of betraying the clones to Leekie because she knows her own motivations and she trusts Cosima to hear her out. It's very clear that she is willing to explain herself for as long as it takes, and that she understands Cosima's anger. And then Cosima attacks the one thing she thought was real for both of them—the one thing that Delphine isn't confident about, the one thing that they both had treasured as utterly, completely real— and it shatters her.
Delphine:*tearful laugh* I had never been with a woman before-
Cosima: Yeah. It showed.
The way Cosima just gives a horrible, low, wordless wail as soon as the door closes behind Delphine. You can tell her whole world and all the hopes it had contained just walked away from her.
Helena crying and screaming as she tries to escape the cage, finally managing to get to her phone and immediately calling for help. She turns instinctively to Sarah... who shows up and puts a gun to her head.
Her first words when she's forced to call Sarah are a desperate "Is Kira all right? ...It was an accident!" She would never hurt that little girl, and everyone is convinced she would. And when Sarah shows up, Helena swears she will never try to see her 'angel' again. What happened to Kira wasn't her fault, but she feels like it was...
The look of utterly miserable resignation on her face when she thinks the one person she wants to like her is about to become her murderer is awful.
Helena: *dully* Do it.
"They patented us."
Cosima's horror is bad enough, but the look on Delphine's face when she realizes the true depth of what she was a part of...
"You killed the woman I've been dreaming of my whole life!"
The death of Helena. We all knew it was going to have to happen, but nobody expected it to be so soon, or so sudden. And the fact that even as she stands there covered in blood, having just beating the ever-loving crap out of Sarah, with absolutely nothing left to lose, Helena is still lost and confused and afraid. She only ever wanted to be loved... but she's too dangerous to be allowed to run free with no one to control her, and she doesn't understand.
Helena is like a fighting pit bull. She had it in her at birth to be an absolute sweet-hearted angel, to have just as much capacity for love as Sarah or Cosima; but she was beaten and abused, kept in cages, forced to become a killer because it was only when she killed that she was shown any kind of affection or approval. She hurts people, and she can't stop, and it's not her fault because she's like a child, in pain and confused and not understanding what love is. The only kindness Sarah could show her was putting her out of her misery, exactly as you would with a pit-fighting dog that can never be re-homed because they don't know how to not hurt people.
After her confrontation with Helena, Sarah returns to Mrs. S's to find the whole place trashed and empty. She runs upstairs calling for Mrs. S only to find that she and Kira are gone.
Even worse when you consider that everything Sarah did was to keep Kira safe. She almost went with Rachel Duncan for her.
"I want to know that my daughter won't have to live like this."
The music. The downbeat song just makes the end of the finale more emotional.
Aynesley's death and everything that lead up to it. She was completely innocent in everything and had no idea what was going on - all she knew was that her once best friend kept finding new ways to betray her for no discernible reason, culminating with her death by Alison's negligence. Made even worse by the fact that Alison let her die for no reason at all (as far as the viewer is concerned). Aynesley was moving away. Even if she was Alison's monitor, Alison would never have seen her again anyway.
During her arrest, there's a brief moment when Sarah locks eyes with her daughter, fear and shame plainly on her face.
Later, Kira says the whenever the police come, mummy goes away. No wonder Mrs. S thought Sarah was a bad mother.
When the wall that Cosima's been holding up against Delphine finally comes down:
Cosima: I'm sick, Delphine.
Alison and Donnie toward the end of the season one finale. She's feeling horrible about Aynesley's death but he comforts her and tells her he loves her. Just as Alison starts feeling better, Donnie leaves to meet with Dr. Leekie. Alison's husband, the man she loved since high school and raised her children with, has betrayed her.
Mrs. S. being forced to kill her confidants, whom she has known for years, because they had betrayed her. And her haunted look when Sarah and Kira drive off without her.
Mrs. S.: Could you just tell me why? After all we've been through together — why?
The woman is rather sad in her final moments. She shakes and stutters, her hands impaled by knives on the table, as her old friend shoots her at point-blank range.
Alison's grief and guilt over Aynsely's death lead her to drinking more and more. Then she learns that Donnie is her real monitor and that Felix and Sarah are skipping town, leaving her alone.
Jennifer's video diaries. In the first one, she's bubbly and optimistic that her health will improve. But in the second one, she's horribly ill, thin and pale, her hair has fallen out, and she's been disillusioned about her chances of survival.
Jennifer: I'm going to die here.
While watching Jennifer's diaries, Cosima is very aware that if her efforts to find a cure fail, she's watching her future. She has the same reaction to seeing Jennifer's body on an autopsy table.
Felix deciding to part ways with Sarah once she starts staying with Cal.
Felix: There's no place for me here.
Sarah tearfully telling Kira about how confused she felt growing up without any parents, making it clear that she doesn't want the same thing for her daughter.
The ending of Governed As It Were By Chance. Sarah is knocked out by Daniel and wakes up zip-tied to a shower. He pulls out a razor and starts cutting her behind her ear...when a noise interrupts him. He leaves the bathroom and is attacked, managing only to stumble back into Sarah's view bloody and near death. Helena appears like a ghost in a Blood-Splattered Wedding Dress, prompting Sarah to scream even more than when she was being attacked. Helena slowly inches toward her sestra begging for help and gently embraces the crying, terrified Sarah.
Helena's Wham Line: "I think he took something from inside of me..."
Near the end of Ipsa Scientia Potestas Est Sarah tries to stop Helena from killing Rachel with a sniper rifle, telling her that she needs her help. When Helena claims Sarah just wants to use her, Sarah tearfully tells her how she felt after she had shot her.
Sarah: I thought I killed you. I couldn't tell anyone what I lost. You came back. Please put... put the gun down.
Helena: You make me cry sestra.
Everything, absolutely everything, about Ethan Duncan. Sarah finds him a cluttered, slightly rundown old house where he lives under the Birdwatcher's protection for twenty years. One of the creators of the clones is a sweet, frail, slightly forgetful old man who made too many mistakes and now lives in fear for his life. When he first sees Sarah, he asks if she's his daughter Rachel. Then he reveals that Leekie killed his wife in the fire and was forced to fake his death; all the while his precious daughter was being raised into the cruel, cold woman who's currently trying to ruin Sarah's life. He loved Rachel so much and he completely lost the chance to watch her grow up. That's all he and wife wanted, to have a daughter and raise a family. And now all he has are his little birds.
Sarah telling him about the other clones, Alison and Cosima, that Cosima is sick, and practically demanding his help because she just feels so overwhelmed by the conspiracy and all that has happened to her.
Felix drunkenly admits to Art that that he's tired of helping Sarah and hates being the guy who always gets kicked in the teeth by life because of his sister.
Helena expressing a desire to be a mother and quietly leaving with Gracie and Mark so Hank can return the fertilized eggs to her womb.
Rachel reunited with her thought-to-be-dead father and learns the truth about her mother's death — that the man who raised her was responsible. Despite making arrangements with Marian Bowles to eliminate him, she warns Leekie because she does still care for him. Leekie looks genuinely heartbroken when he hears all this.
You actually feel a little sorry for Donnie when he finally learns everything that's going on and exactly the magnitude of his betrayal of Alison.
Alison: You destroyed us Donnie, with the spying and the lies. I love you so much and you ruined our family. And you're so stupid you don't even know why.
Rachel decides to keep her relationship with her father strictly professional, even calling him by "Professor". His disappointment is palpable.
Rachel learns that the clones are barren by design and goes on a mental frenzy. On the outside, she remains cool and controlled, but on the inside she imagines going on a rampage and destroying her office.
At the end of Variable and Full of Perturbation, Cosima suffers a coughing fit that suddenly turns into a full-blow seizure that leaves her on the floor gasping for breath as she chokes on her own blood.
Rachel's Villainous Breakdown is surprisingly poignant, especially when she starts to cry while starting at a picture of Sarah and Kira. If it wasn't clear before, it's clear now that she really wants to be a mother, but that option was taken away from her a long time ago.
Sarah is very reluctant to subject Kira to an invasive procedure to save Cosima's life. Then her horror when Rachel attacks Felix and kidnaps Kira. This time, it's not a ploy by Mrs.S - Kira is really gone. No matter what Sarah does, her family is always in danger and there's nothing she can do about it short of giving up all her freedom and becoming a Dyad puppet.
She does become a Dyad puppet in the finale, throwing away her freedom and privacy for a chance to be with her daughter. Every second of it is heartbreaking.
Rachel admits to her father that she rewatches old tapes of her childhood because she forgot how it feels to be loved. Then Ethan commits suicide by poisoned tea to keep her from accessing his scientific knowledge of the clones because, even though he loves her, he knows she'll abuse that knowledge.
Ethan's last words were pretty much him lamenting what happened to his daughter.
Ethan: My poor poor Rachel.
The Kick the Dog moment of Delphine getting sent to Germany by Rachel was pretty sad too, especially since for all Delphine knows, Cosima's going to die, and she won't even get a chance to say goodbye. No matter what you think of Delphine's motives, it's pretty clear that she's genuinely in love, so Rachel's cruelty just hurts.
Helena's dream about her sisters throwing her a baby shower, because then it fades to her waking up in a crate talking to an imaginary scorpion.
Sarah's horror and fury when she learns that Mrs. S traded Helena away. She practically begs Sarah to understand, but Sarah just screams at her and storms off.
Sarah: You're not my people.
Delphine breaks it off with Cosima due to work, both of them barely holding in their tears.
Just when it seemed like Sarah, Kira and Cal could all move into Cal's new house as a family, Rudy threatens Kira with a gun. Fearing for her daughter's safety, Sarah sent her away to Iceland with Cal until the threat of Castor has passed. Its absolutely heartbreaking to see this family lose their second chance at being together.
Art confesses that he feels responsible for Beth's death because he didn't pick up on the signs that she was suicidal. And that he was in love with her.
This makes re-watching the pilot episode very painful. Art was the last person Beth spoke to right before she killed herself. Just minutes later he called back, but she was already dead. He wouldn't know that the woman he loved had died until weeks later.
Bonnie nearly kills Mark, which is made all the more painful with Gracie worrying that he might not come back.
Sadly now its unclear if she still wants to be with him anymore, since she found out that he was clone. In the next episode, Gracie takes off her wedding ring.
Gracie has a miscarriage and is exiled. Her own mother tells her that they only wanted her for what was in her womb, that she was being punished for running away, and without the baby she's worth nothing to them.
The sight of Abel Johanssen's bones after Sarah digs up his grave. He was just a baby...
Helena and Sarah's reunion in 3x05 counts. No heartfelt moments, just a lot of misunderstanding on both sides.
It seems as if Sarah and Helena will escape from the Castor base together. However, Helena's blames being given to the military on Sarah and abandons her in her cell, escaping the base by herself. Sarah's face when she realizes that she's being left behind by Helena is heartbreaking. Later, as she's escaping the base, Helena admits to Pupok that she feels conflicted at the thought of leaving Sarah behind.
Helena: My sestra. She tears my heart.
Paul's death just stunned the entire fandom. After getting fatally stabbed by Miller while trying to escape Castor HQ, he finds Sarah a way to safety and tells her to go on without him, then confesses that he's always loved her. Bleeding heavily, he manages to make it to Coady's lab and confronts her one last time about what's she and her sons have done to multiple innocent women. She shoots him for it, but then he lets his grenade fall...and its over.
Several of Sarah's hallucinations, liking chasing after Kira. But the most heartbreaking of all: Beth. Sarah has an imaginary conversation with the woman whose life she stole so long ago, wherein Beth discusses her life and death, obviously bitter about the terrible hand she'd been dealt.
The flashbacks of Beth and Paul's life together, especially knowing that he was never in love with her. Still, he feels guilty about the fact that his deception led to her suicide.
Delphine and Cosima not getting along anymore, then Delphine brokenly admitting that she still misses her.
Felix shows a surprising cruel side when he ruthlessly taunts Rachel about her missing eye. He then comes close to breaking down, showing that his nastiness is just an expression of his fear for Sarah's safety, but it doesn't help when Rachel starts to cry.
Rachel painting with a childhood picture of herself and her father in view.
Mrs. S and Felix are hiding the fact that Sarah's missing so Kira won't worry. She was afraid that her mom wouldn't talk to her because she was angry, but Mrs. S and Felix swear its nothing serious.
When Gracie overhears that the Castor clones are mayflies and realizes that Mark might die soon.
The reveal that Krystal, one of the most endearing characters on the show, was kidnapped, placed in a medically-induced coma, and used as a body double for Rachel. Just earlier in the episode, Sarah tried to kept her out of the conspiracy out of compassion, but it's partially Sarah's fault that she's in this situation.
When Mrs. S. finds her old friend Terry dying and with his last words, he tells her that the prisoner she's looking to kill is actually her own mother.
Cosima tries to reconcile with Shay after what happened with Delphine, but Shay kicks her out anyway.
Helena recalls that she was made to shoot a puppy when she was nine.
Helena staying with Rudy as he dies is possibly the most tender time the words "you were a rapist" were ever spoken
Delphine's tearful goodbye to Cosima, before she ends up getting shot in a parking garage.
Delphine: Give your sisters all my love.
During Alison's dinner party, Sarah raises a toast to Beth.