Exactly! Once you start doing actual bf-gf dates (dinner, minigolf, hiking, parties etc), it sorts itself out pretty quickly. The girl will either ask you to be bf and gf or just ASSUME that you already are. You have a few options if the girl just ASSUMES you two are exclusive. You can play dumb and keep banging other girls until you mess up and she finds out. She will be hurt and of course want exclusivity. Kind of a dick move, been there, done that.
Or you can bring up the relationship talk once you KNOW for sure, she's crazy about you. If a girl is blowing up your phone, enthusiastically meeting up for dates and sex, believe me, she's not having sex with anyone else - she's not even thinking about it, so the relationship talk is more of a formality instead of coming from a place of weakness.