okay so 4.2 and the main plot of that and how it affected neuvi both during and after. read at your own peril, it will contain spoilers.

first off, neuvillette feels nothing short of pure guilt for being the mastermind behind uncovering the truth. he heavily assumed that furina was being the way she was because she forgot how to drop the mask, not that she cannot drop the mask, as for the last five hundred years, that is how he knew and viewed her - a being of pure flamboyancy and somewhat immature to the truth that fontaine is destined to flood, and she will be alone in the end - but he still tried to trust her.

so watching the trial, watching furina crumble and crack and just break in front of her, neuvillette's guilt began to rise, but he must keep a stoic face in the courtroom, and that is killing him. in the pursuit and name of the truth, neuvillette had shattered everything that furina built in focalors' request, and broke the trust he and furina had built for so long.

he doesn't even have time to comprehend it, because the next thing he knows, the oratrice holds more secrets, and neuvillette is facing a truth he never expected or, in hindsight, really wanted - meeting focalors to witness the execution. he didn't wish to meet focalors because the moment he did, he knew it meant disaster, because that meant this was the final act of her charade - a charade he was quite definitely the leading male in.

neuvillette wanted so many answers because he was playing a role he never knew he was playing until its last moments, and this is his biggest regret. he should of spent time with focalors as a person, not interrogate her in a way, but he already ruined furina, he knew focalors was fully aware what he did and expected malice from her. yet, all he got was her serenity and gratitude. this is the double edged blade of the truth. she was glad he played his part, but neuvillette isn't happy he did it. he knew he had to when focalors said it was the intended ending, but it never meant he had to like it.

so her giving up her divinity and life, so he can become the fully fledged dragon sovereign he has waited over one thousand years to be, it isn't pleasant, it will not be pleasant for a while. yet, it's a necessary move for the future. he too, like focalors but on a much grander scale, despises the heavenly principles, for many reasons, and will use that power returned to him by her to finish what she likely wanted to start. the tears he sheds, knowing that furina will stay when focalors is gone, are for focalors' self-execution and the damage he has done to furina. his self-imposed guilt is the gavel that declares fontaine innocent of egeria's sin. he will carry that guilt instead now, for damaging furina and being the execution's witness.

when everything settled down, fontaine rebuilding itself, he does actually keep the room furina used in the palais mermonia the same shape she used to. she doesn't stay there anymore, and for her mental wellbeing, that is necessary and valid to him. yet... it is a habit he cannot break. despite everything, neuvillette will always see furina and focalors as a platonic soulmate, the yang to his yin, and he has ruined a half-millennia friendship in the name of the final act of the masquerade. it will take time for him to accept this is a necessary thing, but he knows he cannot face furina for a while, not unless he absolutely must for a bit. he will leave the fate of their friendship in her hands, and respect her choice.