The new Vincent — the one who had learned that he didn't need to be a lone God, that he could literally and metaphorically reach out to somebody — was snuffed out.

Alastor annihilated Vox's redemption and transformed it into a new, even worse, corruption arc. (10/10)

Why should he share the spotlight again? Why should he let other people get close to him when there are no friends in Hell anyway? When any connection makes you needy and weak? Somebody to be mocked?

In that moment, all the progress Vox had made was erased. (9/?)

That's the final nail in the coffin, what throughly humiliates Vox.

His willingness to share the spotlight is shameful, the fact that he for once hadn't tried to kill a competitor but had instead admired and befriended him is a HUGE mistake, something that makes him dumb, weak. PATHETIC. (8/?)

So he tries to salvage it. He says "I just thought, since we were friends..." as a way to explain himself, and it backfires when Alastor says that there are no friends in Hell, sounding genuinely angry."I thought it was something you understood. How embarrassing..." (7/?)

"And here I thought you might be approaching my level. But asking for asssistance? A partnership?"

This tells Vox that Alastor sees him as inferior, that asking for help or wanting to work with someone is shameful. His mouth trembles when Alastor says he's disappointed in him. (6/?)

But when he proposes to become partners Alastor calls him pathetic, weak, he says "YOU need ME to join your team", which in Vox's mind could easily be read as "You need me, I don't need you". (5/?)

He admires Alastor, thinks he is INSPIRING. He wants to rule Hell WITH Alastor, he doesn't see him as competition and he clearly doesn't want to eliminate him.

He seems to be starting to go against what caused him to end up in Hell in the first place. (4/?)

They have been close for a few years before Vox even tries to propose a partnership. He looks shy and excited, buzzing and blushing. This is not an attempt at manipulation like he would do in the future, or did in the past.

Something about meeting Alastor and growing close to him changed Vox. (3/?)

Alastor. In both cases.

Vincent had always wanted more, killing his competition to climb higher and higher, never caring about who were essentially stepping stones on the path to literally become the leader of a cult. But with Alastor we don't see that. (2/?)