@Aurosandro Right, but they made a promise when they were kids and as we all know, people change by the minute. It's not like they were dating either, they just liked each other, so she wasn't bound to him and this is life man, people starting to like other people after long interactions happens. You could say "Oh but this is fiction, not reality! The author doesn't need to make it so painfully realistic" and I'd agree, but everyone has different ways of doing things.
I despise NTR and NTR situations like every sane person, but in Sono Mono's WN case, I don't really care much about it simply because Wazu has a pretty damn solid harem anyway so who cares about a bitch or two? It's not like he's left with crumbs like in pretty much every depressing NTR work ever.
I do have the mentality of the WN being unfinished products because let's be real here, they are. However, thinking it's not canon is dumb since the author is the one who decides what's canon or not, whether we like it or not. With that said, the LN is the true canon just because it exists (it's the finished product) and decided to change things around. It's true though we don't know the real vision of the author, if he changed it because he also changed inside and thought it was a dumb, blackpilled idea in the first place, or because the big boys wanted him to change it because it's unnecessary (which is also true). Anyway, we can be happy just knowing that the LN fixed things, can't we?
Ending my thoughts here. I don't think Wazu is braindead for what he did, at all. Look around, every person in love has made or will make stupid decisions at least once in their lifetime, maybe not radical like Wazu's, but still.