It's the adjectival form of the word "affect" in its noun sense, meaning "mood" or "feeling". This form is pronounced differently: A-fect (emphasis on the first syllable, with the vowel like in "rat").

"Affective polarization" is "people being polarized in how they feel about each other", i.e. animosity towards people in the other party. It's a technical term used by sociologists and not in common use, but it's not a typo.