possible_mutual_interest_trigger

possible_mutual_interest_trigger = {
	$CHARACTER_1$ != $CHARACTER_2$ #Cannot be an event target for yourself
	$CHARACTER_1$ = {
		OR = {
			has_relation_crush = $CHARACTER_2$
			has_relation_lover = $CHARACTER_2$
			has_relation_potential_lover = $CHARACTER_2$
			has_opinion_modifier = {
				modifier = love_opinion
				target = $CHARACTER_2$
			}
			# Not related etc.
			NOR = {
				any_sibling = {
					this = $CHARACTER_2$
				}
				any_parent = {
					this = $CHARACTER_2$
				}
				any_child = {
					this = $CHARACTER_2$
				}
			}
			AND = {
				$CHARACTER_2$ = {
					is_ai = no
					has_perk = subtle_desire_perk
				}
				age >= 20
			}
		}
	}
	$CHARACTER_2$ = {
		OR = {
			has_relation_crush = $CHARACTER_1$
			has_relation_lover = $CHARACTER_1$
			has_relation_potential_lover = $CHARACTER_1$
			has_opinion_modifier = {
				modifier = love_opinion
				target = $CHARACTER_1$
			}
			NOR = {
				any_sibling = {
					this = $CHARACTER_1$
				}
				any_parent = {
					this = $CHARACTER_1$
				}
				any_child = {
					this = $CHARACTER_1$
				}
			}
			AND = {
				$CHARACTER_1$ = {
					is_ai = no
					has_perk = subtle_desire_perk
				}
				age >= 20
			}
		}
	}
	$CHARACTER_1$ = {
		matching_gender_and_sexuality_with_trigger = { CHARACTER = $CHARACTER_2$ }
	}
	$CHARACTER_2$ = {
		matching_gender_and_sexuality_with_trigger = { CHARACTER = $CHARACTER_1$ }
	}
}

As written in game/common/scripted_triggers/00_romance_and_seduction_triggers.txt.