More than just ‘Jealousy’ (although that’s certainly part of it), I think one of the big through-lines of Chapter 5 is ‘You Can’t Make Someone Love You’. That relationships are complicated and mutual things dependent on personalities and history, and can’t (or shouldn’t) really be ‘forced’. That’s part of the reason for the constant Dating Sim references this Chapter, and it’s something that’s been kinda brewing through the whole game so far. It connects to the recurring ideas of deconstructing video game tropes (notably here the gamification of interpersonal relationships) and your choices not mattering, and also Divorce. How Asgore constantly fails to make Toriel ‘feel what she used to feel’ for him and probably making things worse through these constant attempts.
And to Ralsei’s original naïve ideas of ‘how to be a friend’. Them thinking it’s a simple matter of always ‘being nice’ - paralleling ‘Relationship Mechanics’ in games that are mostly about choosing the friendliest and most placating options, and that's really all you need to 'max out' your relationship with whoever.
Only for them to realize that it’s more complicated than this as they grow closer to Susie, someone who absolutely is not the person who chooses only the ‘nice’ options all the time, and realize that they love her for it. But also at the same time, their sweet and passive demeanor seems to have pretty much failed to endear them to Kris, despite their best efforts.
That relationship only progresses when Ralsei stops trying so hard to be Lovable….
And then also Our Choices Don’t Matter meaning that there’s no Choice a Player can make that can meaningfully change Kris’s most important relationships. These relationships also don’t depend on simply picking ‘positive’ options (because if one likes Kris, that also goes hand-in-hand with liking some amount emotionally detached teasing and pranks). AND the most important moments of relationship development happen of Kris’s own volition, and they will rebel against words that are either too cruel or too sappy to their own taste. Which in previous Chapters was mostly a positive, hopeful thing. No matter our influence, Kris’s friends will always be Kris’s friends first and foremost. We don’t have enough power to ruin their most important relationships or to make their friends love them for something that they’re not.
But in this Chapter, there’s a new melancholy wrinkle added to it. Through the whole Festival Sequence, you’re presented with a bunch of choices that under standard ‘Game Logic’ might be expected to influence the relationships between Kris, Susie and Noelle - but in true Deltarune fashion, regardless of your choices, Susie and Noelle always start their romance at the end of it. But while this could be a heartwarming story about Cute Teenaged Lesbian Love triumphing over a manipulative Amoral Time God… the whole situation also makes it very clear that even if Kris was able to make choices freely, there’s nothing they could choose that would make Susie love them either. No matter how close they and Susie get, she just doesn’t seem to be attracted to them that way.
You can also add to it the way the Flowery Final Boss plays on the ‘Power of Friendship’ bit that’s generally expected at the end of a Pacifist Run…
Where Flowery has his own Recruits that instead seem to team-up with Flowery and against you, regardless of your choices. Because the cute little ACTs you did to Recruit them were nice and all, but were they really enough to make them truly love you more than they already loved Flowery and the other Flowers? More then they loved their Dark World?
And then there’s Flowery’s whole thing. Like in many other aspects of their characters, he and Ralsei are two sides of the same coin. If Pre-Character-Development Ralsei is like someone who tries to please and befriend everyone in an RPG, Flowery is someone trying to powergame his way through a dating sim. His (and the other Flowers) constant showering of Asgore with admiration, gifts and ideal hang-outs/dates that are all just perfect for him are partly just trying to repay Asgore for the kindness he’s given them and making him happy… and also to try and make Asgore choose Flower Kingdom and his Flower Family over Hometown and his Light World Family.
As much as Flowery teases Ralsei over their jealousy of him, his behavior often reveals that he’s jealous of Kris, for being part of that family that has, from his perspective, have given Asgore nothing but grief, and yet he still seems to love more than the Flowers. Kris is a living demonstration of how his gifts and dedication to Asgore is secretly just as ‘useless’ as his fake made-up overpowered stats. Flowery is also well aware that Kris is the one that opened the Fountain in the first place, and that they seem to have some sort of hidden agenda that’s not beneficial to their dad, and Flowery still feels like Asgore will always choose them over him.
And, well, the resolution to the Flower Kingdom arc is a mixture of that (especially considering how much he was motivated into exploring the Dark Worlds out of a belief that it will magically make his family life ‘go back to normal’…. Literally pushing the Flowers away for the sake of that goal...)
But also, it’s kind of a matter that Asgore does absolutely love the Flowers, just not in the way they wanted to. The Flowers wanted Asgore to love being around them so much, he’d choose their fantasy even if it means their deaths, but Asgore loved the Flowers so much that he wanted them to live.
And in way, that’s also kind of a mirror to Kris’ situation with Susie. She definitely loves Kris, they just feel like she’d never love them the way they’d want her to.
And then, the way Pink interacts with the whole Dating Sim Pastiches adds in some wrinkles of important nuance. She’s the one notable occasion (well, outside of the other even bigger exception we’d get to in a moment) where the Gamification of Relationships is actually useful, both for the Player to progress and beat the Fight and for Pink’s Body and Ghost to solve their relationship issues. In a way, it’s kinda like saying “Well, of course, just because you can’t make anyone love you, that doesn’t mean Choices don’t matter at all in relationships, obviously. Making Choices of consideration and healthy communication is important.”
And even then, part of the resolution is Pink’s Ghost accepting her Body’s needs even if it means she won’t necessarily have her all for herself. She there’s still there’s this undercurrent of accepting that you can’t make people love you the way you want them too.
But, of course, the biggest and obvious exception of the concept of ‘You can’t make someone love you’ is, well, the same as what seems to be the biggest exception to the concept of ‘Your choices don’t matter’, and that’s the Weird Route, of course.
The Weird Route is the one exception to the idea that we and our choices can’t have a meaningful affect on Kris’ relationships, and it very intentionally uses a lot of the Tropes and language of, like, going on a Romance Route with a character in a Video Game, complete with a supposed ‘climax’ when said NPC decides to invite you to the big romantic Festival, and it also uses every storytelling tool in its disposal to showcase how it’s utterly creepy and manipulative and wrong.
It’s adding to the point of ‘you can’t make people love you’ with ‘also, even if you can make people love you, you probably fucking shouldn’t”.
But I suppose, in many ways it is still a case of one not being able to control how people love them…
