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.
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 BSOD 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.
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.