Episode 42. The whole episode is Charlotte and Lizzie's argument. Pursuing an advanced degree? Having accepted a lucrative yet not perfectly satisfying job? Abandonment? It's obviously tear-jerking in-universe.
Lizzie: I know that if you take this stupid, mind-sucking, pointless job that you'll never have time to work on your own stuff anymore.
Charlotte: Well, that's no different from right now. Because guess what, Lizzie? All this time I haven't been working on my stuff. I've been working on yours!
Charlotte: *quietly* If you need help with the videos, I... I can recommend some people.
Becomes even more of a Tear Jerker with the follow-up in The Secret Diary of Lizzie Bennet, where Lizzie writes in her diary about the event, and the follow-up is the shortest diary entrance yet, only four sentences:
It didnít work. Charlotte is gone. She walked away from her degree, from the videos, and from her best friend. I donít know what to do anymore.
The week after that, she writes: "I just wanted to avoid life for a while. Because if I did face up to what happened, Charlotte would really be gone and I would really have been a terrible best friend for not seeing things from her perspective."
Lizzie's occasional sobering realizations of how bad her family's finances are.
Episode 43: "My name is Lizzie Bennet and... I miss my best friend." And then we get to see Charlotte's reaction to it.
Maria's episode 2, where we learn that Charlotte isn't watching Lizzie's videos anymore, and doesn't want Maria to talk about them.
After episode 42, all of Lizzie and Charlotte's interactions become this.
Episode 47: Jane's baffled "What does this mean?" after learning that Bing is going to Los Angeles. Lizzie, having learnt about what happens when you caught hard moments on tape, goes to the camera and switches it off.
Jane's heartbreaking Heroic B.S.O.D. in episode 48, which Jane gave her permission to leave in.
The hints that Lydia might just play cheerful, but is in fact kind of lonely. Shown in episode 12 of her spin-off video blog.
Jane's postcards and texts to Lizzie in Episode 59. It's evident that she's heart-broken.
Lydia implying that an ex-boyfriend is bullying her to the point that she'd rather be with Mary than at home. Then when Mary is sick of Lydia barging into her life constantly, Lydia runs away to LA to Jane, causing a major fight between her and Mary later on. Mary Kate Wiles's face turns Lydia into an instant Woobie many many times.
The fight was sad for Mary, too, because of why the relationship goes so far downhill: She had started to see Lydia as a friend, not just a cousin, but Lydia persistently only hung out with Mary when the older Bennet sisters weren't around, and when she wanted to hang out she expected Mary to drop everything she was doing and comply. Mary didn't necessarily hate Lydia's company as much as she hated the one-way factor that Lydia was pushing on their relationship, and it made her cut herself off from her cousin completely. Given that Mary seems to have difficulties making friends (which is apparently a Bennet family trait not only shared by the sister trio), that must've hurt quite a bit.
Jane can't even say "snickerdoodles" in Episode 71. She made them for Bing and didn't manage to give them to him because he left the town without ever telling her.
All of Episode 73. If you thought Lizzie and Charlotte falling apart was hard to watch... Lizzie and Lydia argue.
Lydia's post-73 revenge video as well. It's hard to watch someone who is in so much pain.
Lydia and Wickham's abusive relationship's development, from Lydia's spin-off episode 24 onward. When they met, she was confident and gleefully convinced him to take his shirt off for some gratuitous Fanservice. Now, he isolates her from everyone and attacks her self-confidence while she cries on his shoulder.
Episode 29. Lydia announces that she loves Wickham and that it's the only time she's felt good enough for someone. It's like watching a train wreck.
Episode 82, where Gigi tearfully reveals the truth about what went down between Wickham, Darcy, and herself.
Episode 84, when Lizzie discovers that Wickham intends to publish a sex tape featuring himself and Lydia. She breaks down and starts to freak out and Darcy insists on getting her on the next flight home. Examine Darcy's face. He's not only disappointed that his one chance at asking Lizzie out in an actually nice way was ruined, but he knows exactly what she's going through right now because that's what happened to him.
The lead up to the reveal of the sex tape; before, Lydia was constantly tweeting in defence of George, saying that he cared about her and that the followers should just leave him alone, even going so far as to say 'why would I need [friends] like that? After the reveal...her account is silent, at first. No defense of Wickham, no opinions, nothing. Just 'likes' of tweets that bash Wickham and telling her she's being naive and idiotic, now agreeing with her detractors...
Her tweets to Wickham to pick up his phone and talk to her, to tell her that he didn't do it, reminding him of 'the sunset', pleading with him...and he unfollows her.
Episode 85, with Lydia's choked sobs, desperate denial, and horrified scream after discovering the website.
Episode 86, as Lizzie is desperately trying not to break down on camera and Jane tries to reassure her, saying the only they can do now for Lydia is to just be there for her. Especially since Jane had quit her job to come back. They had to tell Mr Bennet. The Adult Fear of the situation is obvious, and although we only get his reaction second hand from Lizzie, her description of his response is heartbreaking.
Dear. God. Episode 87. All of it, from start to finish, is non-stop heartbreaking. For the first time ever, Lizzie breaks down on camera. Jane can do nothing, and knows it. Even Mr. Bennet, who knows about the video, tried to find something with a PI and couldn't. Lydia is down. Down down. Go watch it. Bring tissues. And booze. You'll need both.
Even after everything George did to her - all of it - Lydia still loves him.
"I thought I was, for once, good enough for somebody."
Lizzie: [Wickham]'s a monster. Lydia: No, he isn't, he's... I don't know what he is. ...But I could be... someday...
Another moment for Episode 87: Lydia breaking down and sobbing "Why doesn't he love me?" and Lizzie's immediate "I love you." It's heartwarming, but it also makes you realize how large the gap between them has grown and how little Lizzie can actually do in that moment.
Is Fridge Sadness a thing? Darcy's reactions to the videos after Episode 60 is underplayed, but think of what watching them must have been like. For someone so socially awkward, confessing his love must have been terrifying, and in response he gets actual anger. Then he spends several hours watching a series of videos revealing to him that the object of his affections despises him and has devoted months of her life to informing a very large internet fanbase how obnoxious he is. And as a bonus, he also gets to realise that he sabotaged his best friend's relationship with his girlfriend for no real reason. That must have been a rough night for Darcy.
The Domino video where Gigi finally says "fuck it" and calls Wickham herself, despite her brother and Fitz begging her not to. You can see the fear in her eyes, even when she only gets his voicemail. Wickham is a monster, through and through, and it's clear Gigi's still deeply wounded by what he did to her.