#sho spent all of neo being like 'wow im sure glad time travel means i wont have to face consequences of my actions'

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i don't even get that sho betrayed the wicked twisters. he told them that he was just helping temporarily. and he did that. and then he left. what was the betrayal exactly lol

It's not about him leaving the W.T

This is semantics and I really don't feel like going and picking over neo to double-check, but I don't think Sho ever implies that his help is temporary as much as it is sporadic. He comes and he goes, but from the W.T reactions to his permanent departure it certainly doesn't look like they were expecting him to stop coming back. Nagi is desolate. Rindo says that they're doomed. Heck, this is the moment where Fret's cheerful mask slips for the first time in the game! And anyways, regardless of what Sho did or didn't imply, leaving them when they had just learned that they were playing for their lives, going as far as to say "Now I can finally ditch you zeptograms" is a massively dickish move, if not a betrayal in and of itself. Remember, they relied on him. Rindo and Fret especially, they're just kids, and they clearly depended on Sho a great deal, and would've absolutely felt hurt and betrayed when someone they'd come to see as a sort of mentor or guardian sneered and then turned their backs on them right when they need him most.

But I'm actually talking about when he attacks them in Week 3!

And this is more in the realm of personal interpretation. The way I see it, it's incredibly likely that Sho knew or at least could've guessed that Rindo's Soul Pulvis are dangerous fairly early on. He's whip-smart and has an extremely high imagination. Not to mention the fact that he spent all of Week 1 investigating it (which is a whole other can of worms, with him twice, once with the DRS and once with Susukichi, willingly putting the W.T in harms way in order to test his little hypothesis). He should've known that it was a danger to the city. He probably did! But that didn't stop him from waiting and watching it grow so that he could eventually harness the power himself, almost definitely so that he could make another attempt on the Composer's seat.

We know from the Secret Reports that he attacked the W.T in a mindless frenzy, that it wasn't something he meant to do. I don't think he necessarily meant to hurt anyone other than Joshua. He thought he could control Soul Pulvis. He couldn't. And then afterwards he has to scrape himself up off the pavement and confront the fact that he zetta fucked up and now all of Shibuya's in danger of being Inverted. It's like his Taboo Noise all over again, he makes a gamble for the city and nearly ends up dragging the whole thing under (with some help from the Conductor, of course) in his single-minded pursuit of approaching godhood, the difference this time being that he looks at what he's done and realizes that he doesn't want it to be this way. So he helps the W.T. He becomes an indispensable part of their plans to save Shibuya, which, in the end, works because of his understanding of what Soul Pulvis is and how it can be overwritten.

But back to his fight. The way I see it, Sho was a mentor figure to these kids, someone who they trusted to have their backs (at least when the mood struck him, anyways). He abused that position to test a theory. Then he left them, right when they were at their most vulnerable. Then he came back, to help them, they think, until he absorbs a power that he knows is highly volatile, attacks, and nearly kills them. Beat outright tells them that Sho doesn't care about anyone, but himself. I think this is wrong, I think he does care about the W.T. There are multiple times when he helps or guides them even when there's nothing immediately in it for him, seemingly because he really does want them to have a shot at making it out of this game alive. I just think that he still cares about himself a little bit more.

The Secret Reports outright say that Rindo is terrified of Sho after his fight. Whatever his motives were, whatever he meant to accomplish, it wouldn't really matter that much to Rindo, or any of the other Twisters. They trusted Sho, and he broke that trust. They (or at least Fret) seem to come around to him again a bit later in the week, but they're obviously more standoffish and nervous around him than they were before. If it wasn't a betrayal in a textbook sense, I think the W.T definitely took it as one.