I think people subconsciously seek out their dual seeking function from other people even if they aren't in a serious or "official" relationship with them. You can receive your dual seeking function from other people in social conversations without putting a neat bow on things and telling the world 'we're in a relationship now' etc. Especially when only certain sexual orientations or race combinations or people from certain economic classes were even allowed to do this for the longest time - not to go all SJW or anything but yeah.

The brain naturally needs a type of duality to create mental peace within yourself - it certainly doesn't mean that you will like every dual you meet or want to marry them etc. The rational dual dyads are usually much better at meeting people and forming life-long bonds with them ime.