Vulcans are touch telepaths, I believe you are aware of this. When we are young, we are paired, through a mental bond, with another who has a similar mental resonance in a way that very much resembles an arranged marriage.
This... arrangement ensures that when a certain amount of growth takes place, the bondmate serves as a...stability. [No way is he explaining Pon Farr to Robin.]

Rarely do to beings meet who share such a mental affinity, that one mental touch can bind them together. This phenomenon is known as T'hy'la... the one person in the entire universe who was meant to be with you. I believe a similar concept exists in the term 'soulmate'.

[Spock shifts uncomfortably...] While T'hy'la are drawn together naturally, that doesn't mean that both parties are necessarily comfortable with one another. Such is the case between the Captain and I.