update_active_consort_opinion_effect

update_active_consort_opinion_effect = {

	# If we currently have any existing consort opinion modifiers, check if they should be downgraded from permanent modifiers to decaying modifiers.
	downgrade_invalid_consort_opinions_effect = { PARTNER = $PARTNER$ }

	if = {
		# If this opinion change was triggered by being divorced/set-aside, we may still technically be married/joined to PARTNER at this moment, but we won't be very shortly and should skip this step.
		limit = {
			NOR = {
				exists = scope:is_being_divorced
				exists = scope:is_being_set_aside
			}
		}

		# Oterwise, apply any new consort opinion effects that are applicable.
		if = {
			# Characters who do not believe in concubinage, but are forced into it, have the harshest opinion penalties.
			limit = {
				is_concubine_of = $PARTNER$
				NOT = { rite = { rite_has_doctrine = doctrine_concubines }}
				NOT = { culture = { has_cultural_tradition = tradition_concubines } }
			}
			if = {
				# Harshest opinion penalty if they are a concubine but believe in monogamy
				limit = { rite = { rite_has_doctrine = doctrine_monogamy }}
				add_opinion = {
					target = $PARTNER$
					modifier = concubine_with_monogamous_faith_opinion
				}
			}
			else_if = {
				# Lesser-but-still-harsh opinion penalty if they are a concubine but believe in polygamy
				limit = {
					OR = {
						culture = { has_cultural_tradition = tradition_polygamous }
						rite = { rite_has_doctrine = doctrine_polygamy }
					}
				}
				add_opinion = {
					target = $PARTNER$
					modifier = concubine_with_polygamous_faith_opinion
				}
			}
		}
		else_if = {
			# Characters who are legitimate spouses of their partner, but do not approve of their partner's other spouses/concubines, will have milder opinion penalties.
			limit = {
				is_spouse_of = $PARTNER$
				$PARTNER$ = { any_consort = { count >= 2 }}
				NOT = { rite = { rite_has_doctrine = doctrine_concubines }}
				NOT = { rite = { rite_has_tenet = tenet_polyamory }}
				NOT = { culture = { has_cultural_tradition = tradition_concubines } }
			}
			if = {
				limit = {
					$PARTNER$ = { any_concubine = { }}
				}
				add_opinion = {
					target = $PARTNER$
					modifier = spouse_does_not_believe_in_concubines_opinion
				}
				#Remove the opinion modifier if you flip-flop and go get concubines after getting rid of them all...
				remove_opinion = {
					target = $PARTNER$
					modifier = spouse_does_not_believe_in_former_concubines_opinion
				}
			}
			else_if = {
				limit = {
					NOR = { 
						culture = { has_cultural_tradition = tradition_polygamous }
						rite = { rite_has_doctrine = doctrine_polygamy }
					}
				}
				add_opinion = {
					target = $PARTNER$
					modifier = polygamous_marriage_opinion
				}
			}
		}
		#Same-sex not accepted penalty
		if = {
			limit = {
				allowed_to_marry_same_sex_trigger = no
				sex_same_as = $PARTNER$
			}
			add_opinion = {
				target = $PARTNER$
				modifier = same_sex_with_no_acceptance_opinion
			}
		}
	}
}

As written in game/common/scripted_effects/00_marriage_interaction_effects.txt.