Consider, if you will: "Failed Marriages, the Arc"

So let's pretend for a second that the Erins are not outright allergic to the possibility of ending a character's arc without them head over heels in loooooove or at least wanting a relationship. (Okay, Shadowsight exists. What a lad!) Say they wanted to portray relationships that just don't work out, and want an arc to have a theme revolving around failed marriages. The current arc seems perfectly lined up for it.

First off, you have the most obvious elephant in the room: Bramblestar and Squirrelflight and their marriage. They've had it tough for ages, but it's really at its worst here. Their arguments are pretty much at their worst since Twilight, except even worse than THAT because they're much older now and supposed to be better than that. They should be trusting each other more, yet Bramblestar is finding himself getting undermined by Squirrelflight yet again and Squirrelflight is finding that Bramblestar is now feeling petty enough to play the secrets game too. Furthermore, Bramblestar is clearly in a mental decline of some sort, and Squirrelflight very much does not have the patience needed to see him through it. At this point, their relationship is at an all time low. If this was the theme, there would be no better time for one of them - or both of them - to say "**** it, I'm done", take a break, and realize that they're doing better when they're not constantly at each others' throats.

Then we have Nightheart and Sunbeam. You already know the drill. Nightheart is a cynical kid starved for validation who straight up believes he fell in love with a girl because she actually treated him decently when compared to his mother who flips between being awkward with him (understandably so) and resentful towards him for not wanting to be compared to Firestar (unfairly so), his sister who went from his greatest ally and advocate to an unsympathetic bitch who basically responded to his claim that he was leaving Thunderclan with "do it, bitch, you won't", a grandmother who shits on him for every third pawstep he doesn't take to her liking, and a grandfather who... TRIES to be there for him but also isn't mentally there and is also embroiled in his latest spat with the aforementioned grandmother. (Mans can't even get jumped by a squirrel without his clanmates making jokes about Firestar. Hell, it should say something that he doesn't even get respect from squirrels.) Sunbeam isn't nearly as starved for validation, but she's had some pretty shit luck in love due to her crush deciding they don't really have romantic chemistry and then seeing him go on to get with her best friend, who she's also been having problems with. On top of that, she's been feeling increasingly isolated because on top of said best friend and former crush spending less time with her and more time with each other, she's found out that her mother, who she used to respect, is actually a borderline xenophobic bully who will justify deception, fearmongering, and antagonism towards perfectly kind cats just because they're not Shadowclan. So our "main couple" have basically been driven together by a desperate need for validation and hurt, rather than actual chemistry. The question is, can they really handle each other at their worst? They've seen each other arguably at their most sympathetic. But what about when they're mad? Angry Sunbeam tends to withdraw into herself to stew, grows resentful of cats trying to poke their noses into her nest, and is generally inclined to assume the worst of people. Angry Nightheart becomes far more short-tempered, tends to think less kind, more uncharitable thoughts towards others, and often hops to the assumption that he needs to prove something. Sunbeam's anger and silence would constantly needle at Nightheart's insecurities and drive him to double down; Nightheart's anger would drive Sunbeam even further within herself and further amplify her hurt. At least part of the issue is that these two simply do not understand healthy ways to process their anger and hurt. But even one fight, with the two of them as they are, would likely lead to both of them hurting each other in such ways that they're basically locked into their own vicious cycles. Could this resolved by the two of them maturing and figuring out how to be more charitable even when they're upset? Sure, it probably could. But even then, could they really see eye to eye on important matters? Sunbeam is good-hearted and willing to be charitable towards others, but she still mostly traditional land by the book, to the point that Blazefire basically broke up with her because they're too different in that regard. Nightheart is remarkably unorthodox and is willing to discard old traditions on a dime if something new will fit the bill - almost irreverently so, as he demonstrates a general lack of respect to old ideas if he cannot outright see the sense of them, regardless about others feel about them. Their "failed romance" could well end with them deciding that they are better off as friends who mutually respect each other, even if they cannot see eye to eye on certain matters.

Then there's Frostpaw and Splashtail. This is a crazy one. Kind of based on very little, too. She starts with a liiiittle crush on him, and as her plate gets stacked higher and higher, so do her stress levels. And at one point? She outright has a mental break and briefly hallucinates having babies with him named after her recently deceased mother. Frostpaw clearly does not need a mate, she needs THERAPY. But the spooky part about this is how little we know about Splashtail. Well that diving too much into the conspiracy theories that I'm sure most of you have heard or considered by now, we can see that there's a little more to him than what meets the eye. Frostpaw could potentially be having her feelings taken advantage of by an outright villainous character - one who might have been responsible for the demise of her mother, no less. Hard to see how this will play out, but it's almost certain to fail in SOME way.

What if this is it? Do you think this is the arc where the Erins say "to hell with it, our theme for this arc is relationships that don't work out"?