So, if it's not obvious by this point, my favorite Homestuck character is Meulin Leijon. I think she is by far one of the best written characters and a really good example of toxic positivity.
Her entire worldview is based on her feelings. Her need for love, no matter how toxic or awful it is, makes her feel realistic in a way no other characters are. Now, while I don't relate to her in the slightest, I will fully admit that she's an utterly wonderful character and I can understand people who DO see themselves in her, my partner included. She's someone whose life is defined by the love she receives. She needs to be seen as lovable. Her last relationship with Kurloz was so perfect that now she's actively spending time, writing about other romantic relationships in especially raunchy ways because of how much passion her and Kurloz's relationship held and she finds that the only way she can actively express that passion is through the sexual acts in her writing. I mean, even now, she still writes ships WITH Kurloz. But she's so focused on red ships because that's what she and Kurloz had in the first place. Whereas Kurloz focuses on black ships because he's projecting his own hatred and disgust onto his writing. Essentially, Meulin is still clinging onto feelings of the past, turning them into writings of a lascivious nature because that's the only way she can properly express that love she felt.
And in the same way that Meulin's world revolves around Kurloz, Kurloz's world revolves around Meulin.
His whole motivation, his whole reason for even bringing about the destruction of everything, despite his clear feelings of curiosity and wonder for it, is the fact that he hurt Meulin. He's disgusted with himself for it, he's disgusted by the way everyone else treats her. He's possessive and manipulative of her because she's all he has. Kurloz is defined by devotion, whether it be religion or the people he cares for. So him hurting Meulin causes him to spiral, causes him to think that this world, as wonderful and beautiful as it is, is inherently flawed. There's no point in saving it when the one thing that "matters" is damaged, hurt, broken, all because of him. He cannot live in a world where he has hurt something he cares for. Kurloz is also very verbose with his words, speaking literal Shakespearean. He preached about his Gods and Angels for days upon days. To him, his voice mattered. It meant something. Him sewing his mouth shut is symbolic of him saying a final statement. It's him realizing that as devoted as he is to his religion, he's devoted to Meulin that much more. His brainwashing, his manipulation, all of that is FOR Meulin. He's actively attempting to take her to The Dark Carnival with him by brainwashing her to do LE's bidding. Because in a twisted, awful, fucked up way, Kurloz is nothing with Meulin Leijon. His motivations do not exist without her.
I think that fundamentally, Meulin and Kurloz's story revolves around unhealthy obsessions with one another in very different ways. Meulin's obsession comes from a need for love and passion, which she can only express through sexual means. She wants Kurloz because Kurloz was devoted to her in every way possible, he truly loved every single thing about her, which is exactly what she needed. Kurloz's obsession comes from him believing that he is fundamentally worthless. He has absolutely nothing but hatred for himself flowing through his veins. If he is not devoted to something he views as grander than himself, than he is nothing. He wants Meulin because Meulin was that something. Meulin gave him purpose. Meulin gave him worth in his eyes by acknowledging him and how silly and funny he is. Even with Meenah, Meulin talks about all of Kurloz's funny quirks and things she finds endearing about him.
TDLR: Kurloz is Meulin's savior. Meulin is Kurloz's purpose.