The entire scene where Dani and Edmund break up is heartbreaking for both characters. Dani has just confessed that she's attracted to women and can't go through with marrying Edmund. She couldn't bring herself to tell him earlier because she truly does love him in a platonic sense, he having been her best friend for most of her life and she didn't want to hurt him. She also didn't want to disappoint his family, who treated Dani as one of their own and were so excited about the wedding. On the other hand, Edmund is devastated to learn that his best friend and the person he wants to marry lied to him and cannot ever return his feelings in the same way. He lashes out at her in his grief while she tearfully tries to explain herself and it's hard not to sympathize with either of them. And then Edmund storms out of the car without looking... and is fatally struck by a truck as Dani watches helplessly. In an instant, Dani is traumatized and Edmund's whole life is cut short.
Even worse is that Edmund and Dani never got to make amends and Dani is consumed with guilt for what happened. Having a person at the wake say to her that she made him happy until the end just twists the knife.
Owen finding out that his mum has died. The poor man is so heartbroken that he can only stare in shock, and only starts to cry for real when Hannah hugs him and whispers a few parting words of comfort.
Could be considered a heartwarming moment as well, but Flora comforting Owen after the funeral and giving him her "Dead doesn't mean gone" speech. The whole staff listens in silence, visibly touched, and Owen looks close to tears as well when he thanks her. Too bad Peter-possessed Miles had to ruin the moment.
Jamie's attempt to persuade Dani to possess her. After Dani leaves Jamie and seemingly drowns herself in the lake at Bly Manor to protect her from the curse, Jamie goes to Bly and swims down to the lake to find her ghost. She begs Dani to take over her body so they can be together in some form, repeating the phrase "It's me, it's you, it's us", but Dani refuses to do that to the woman she loves more than anything. Jamie is eventually forced back to the surface, sobbing.
"Take me with you," she cried in her heart. "Take me. Drag me down like you did the others." But the lady in the lake was different now. The lady in the lake was Dani. And Dani wouldn't. Dani would never.
Doubles as a Heartwarming Moment; even though Dani's spirt will be stuck at Bly probably forever and she will begin to fade, she won't take Jamie's life from her, nor anyone else's.
In Episode 4, Jamie mentions that she would rather be shot than experience dementia. However, come the end, she willingly offers herself to be the new Lady of the Lake, despite knowing that to become a ghost in Bly Manor would mean experiencing the same symptoms as dementia (losing memories, fading away, etc.).
In episode 5, we have a Day in the Limelight episode for Hannah which is told in Anachronic Order. Throughout the episode, she struggles to remember something as she drifts from dream to dream and tries to comprehend what these visions could mean for her. Towards the end of the episode, she dreams of the time she was led to the well near the edge of the property by Miles (who was, as we would later learn, possessed by Peter) and was pushed into it by him, revealing to the audience that Hannah has been Dead All Along and that the murder took place a few minutes before Dani arrived. However, the really tragic part is this: Owen suggests that they go to Paris together and Hannah initially turns it down before Owen is taken home by Jamie. However, moments later, Hannah attempts to go back to Owen to tell him she's reconsidered, only for him and Jamie to disappear in the dark. As the episode closes, she repeats the Survival Mantra she learned from Dream!Owen: "You are Hannah Grose. The year is 1987. You are at Bly. Miles is ten. Flora is eight" over and over again in order to cope with the fact she can never leave Bly again.
In the same episode, Hannah finds out that her husband, Sam, has been unfaithful. Her betrayed screams before Charlotte finds her is sure to make any person shed a tear, especially those who have first-hand experience with being cheated on.
Owen and Hannah ending up Star-Crossed Lovers: her imaginary conversation with him where she admits that she loves him and bemoans that they'll never get to spend their lives together is heartbreaking.
Hannah: God knows I've tried not to think of you. Very hard, but I've thought of you often. Thinking about the places we would go if we were ever to leave Bly. Where we'd settle. You'd open your restaurant. Make me taste all those wonderful recipes you created in that beautiful, maddening mind of yours. I always think that I would very much like...to spend the rest of my days with you. Listening to your dreadful puns, holding your hand, and... I loved you, Owen. I should have told you.
Owen: What a life we could have had.
Rebecca's story is tragic as well. She wanted to become a barrister but decided to become an au pair to Miles and Flora, secretly hoping that their uncle—who is a distinguished lawyer—would grant her a pupilage. Then, she meets Peter Quint and their destructive romance begins. She initially believes that Peter is a secretly kind man who was dedicated to her and for the longest time, even believed it. Then he seemingly disappears after being accused of stealing money from the Wingrave family, causing her to sink into deep depression. Shortly afterwards, Peter shows up and reveals he's a ghost, and for a while, they don't know how to be together since Peter is bound to Bly and can't move past the property. Then, it's revealed towards the end of episode 6 that Peter had decided to help Rebecca be with him "forever" by drowning her body while he was possessing it. However, during said drowning, Peter flakes out and leaves her to die by herself. That alone is agonizing to watch, but watching Rebecca break down when she sees her own body after death is just devastating.
Another moment with Peter and Rebecca: when she tries to comfort him about his own death, her hand passes right through his shoulder. She holds it together for a few seconds... before she breaks down as well about how unfair the whole thing is. Peter, for his part, is equally distraught, clearly wanting to comfort his girlfriend but being incapable of doing so.
Peter's last visit to his past memory with his mother. He wonders to himself why everyone else seems to end up in happy memories while he keeps seeing the memory of his mother blackmailing him. He initially asks why if he's forced to relive a bad memory, why does he not re-experience his father molesting him. But then he concludes that it was because only as an adult does he truly understand and appreciate what a monstrous thing his parents did to him, as a child he couldn't fully comprehend what was being done to him, partially because his mom did her best to make him think it was normal. Seeing him break down with comprehension about what his parents did is pretty heartbreaking.
Peter persuades Miles and Flora to allow themselves to be permanently possessed by promising they get to spend the rest of eternity in a series of pleasant memories with their deceased parents. And the children, who just want their mum and dad back, agree to it.
The whole backstory of the Lady in the Lake, and of Bly Manor as a whole. It was once the property of sisters Viola and Perdita Willoughby, who were determined to keep it from falling to ruin so as to not let their late father down. To that end, Viola married Andrew Lloyd, a distant cousin (to Perdita's chagrin, as she also had feelings for him) and had a daughter with him, whom she loved and devoted herself to... only to then fall ill with an Incurable Cough of Death. She continued to hang onto life for five years by sheer force of will, during which she became increasingly bitter and lashed out at her family due to the pain of her worsening condition (though, she physically abused her sister due to her jealousy and paranoia that her sister was making moves on her husband - she wasn't). It got to the point that Perdita decided to smother Viola to death after six years of ongoing abuse, and then Arthur married her around half a year afterward because he saw Viola when he looked into Perdita's eyes. Having refused to move on to the other side, Viola's spirit became bound to the chest that she filled with the fancy dresses and jewelry she intended to give to her daughter Isabel. In the meantime, Arthur's finances dwindled and, at risk of losing the house, Perdita opened the chest, hoping to sell Isabel's inheritance to keep them afloat. Viola's spirit then emerged from the chest and strangled Perdita to death. Finding Perdita's corpse, Arthur feared the chest was cursed and threw it into the lake on the property before leaving with Isabel, leading to Viola becoming the ghost in the lake. Viola's feelings of betrayal became so powerful that it became its own sort of gravitational pull, and she would emerge from the water at night to search the manor for her daughter and killing anyone else in her path, her memory fading altogether along with her face over the centuries while keeping everyone else who died on the property (whether by her hands, or by someone else) bound to suffer the same fate.
Viola spent the last years of her life kept apart from her husband and daughter (ostensibly to protect them from catching her illness, though Perdita doesn't seem to care about that for herself), only able to watch Perdita effectively raise her child for her. By the end she's begging to be allowed to spend the night with Isobel just once, like they had done when she was a baby, and Perdita—the one who's just gotten to spend a fun family evening with her and Andrew—says no. And the angrier Viola got, the more Perdita rubbed it in that she was going to die, asking her to think about how she wanted her daughter to remember her. In the end, all Viola could do was leave the dresses and jewels she dearly loved to her daughter, and Perdita took those away too.
Andrew throwing away the chest full of fine dresses and jewelry, which was so important to Viola that she killed her own sister over it. And Isobel helped him do it. They didn't even take it with them and throw it away at their new home, which might have allowed Viola's spirit to go with them too and at least see Isobel again.
The final scene of the series: Jamie going about her routine of filling the sink and tub with water, leaving the door open a crack, and sleeping in front of it. When she falls asleep, Dani's hand is shown resting on her shoulder, revealing that she has been there with her the entire time.
According to the actresses, the reason Dani has never shown herself to Jamie is because she knows Jamie is already mostly at peace, but also because seeing Dani might prompt her to return to Bly and offer herself as host again.
