It’s a direct response to your insistence “it’s just words,” and what it means is, “I don’t want to say those words.”

It’s one fucking sentence, dude. It’s not even a garden-path sentence. It goes ‘I could, but I don’t wanna.’ You can stop hassling me as if I’ve reneged on a promise to do a thing, when the entire premise was, I do not want to do that thing.