can_set_relation_soulmate_trigger

can_set_relation_soulmate_trigger = {
	is_adult = yes
	#Some asexuality handling
	trigger_if = {
		limit = { has_sexuality = asexual }
		trigger_if = {
			limit = { is_ai = yes }
			always = no
		}
		trigger_else = {
			$CHARACTER$ = { is_consort_of = prev }
		}
	}
	trigger_else = { is_attracted_to_gender_of = $CHARACTER$ }
	
	NOR = {
		this = $CHARACTER$
		has_relation_rival = $CHARACTER$
		has_relation_nemesis = $CHARACTER$
	}
	$CHARACTER$ = {
		is_adult = yes
		is_attracted_to_gender_of = prev
		num_of_relation_soulmate = 0
	}
	num_of_relation_soulmate = 0
}

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