This being an anonymous forum, readers always have to take a certain amount on faith. The OP has shared her story and we're responding to it. Sure, there's always another side to every story but all we can reply to is what we've been told.
Also, the language used by partner (which, clearly, we can only assume is accurately reported by the OP, but there's no point responding to anybody if we never believe anything) is very concerning.
"He then came out with this narrative that from now on he’s not going to pander to me, that he said nothing wrong and that he’s going to be firmer from now on".
I would use similar language with a stubborn child, or perhaps a very unmotivated employee, but I would never speak like that to anybody I saw as an equal. Not my friends, not my family, definitely not by partner.
Even if your idea that the OP was causing all the arguments is true, it's still a very dysfunctional way of responding. If he were seriously unhappy, then he should sit down and try to reach a mutual agreement on how to improve their relationship (or he should break up with her if she really is so unreasonable).
What is never ok is one person unilaterally announcing how things will be from now on.