Which one would you choose?

There really is a difference in meaning in AmE. They’re not interchangeable, and a copy editor worth their salt will be able to tell the difference.

“Anymore” is an adverb. “I don’t like pizza anymore. I ate myself sick on it, and now I can’t even smell the stuff without turning green.”

“Any more” isn’t the same thing. “I don’t want any more pizza. I’m afraid I’ll eat myself sick on it.” Here, “more” is an adjective (it modifies “pizza”). If you simply said “I don’t want any more,” “more” would be a pronoun (it stands for the thing you want no more of).

It might help to think “adverb” and “anymore” because both are single words. If you mean the adverb, use “anymore.”

As for the answer to the title question, if this is a complete sentence, then “anymore” is the word you want. “I don’t love you anymore.” (I no longer love you.) If there’s more coming, you might want “any more” — but it depends on what’s coming, y’know? “I don’t love you any more than I love my other three partners.” Or something. You figure it out. Please.