How to have the 'define the relationship' (DTR) chat

You swipe right. You go on a date; it's nice. You go on a second date, and then a third, and a fourth. You're getting along, and maybe you even tell your friends about them. Eventually, you stop dating other people, but you're not sure if they've stopped the hunt along with you. The ambiguity gets to you and it's time to do...