As in, when did the romantic relationship begin? When does it end?

Bonus points, what's the purpose of a romantic relationship to you? Why even get one in the first place?

There is some ambiguity here. If a man and woman marry, did their romantic relationship start when they met? Did it start when one of them saw the other as a potential mate? When both of them did? When they have their first date? Their first long conversation?

And when does it end? What if they stay friends for life? What if only one falls out of love?

Is sex any sort of marker for the beginning and end of a romantic relationship?

Especially when you consider men pretty early on know they want to fuck a woman or not, and how the sexual tension in the air between them represents that.