When do you know you're on your own? When you move out of your parent's home? When you write that first rent check?
First time you deal with an irate landlord, a cranky roommate, or that first car repair? The first time you buy a real bed, like a set of queen matresses, with a frame and a real headboard? Or, when someone breaks your heart, betrays your trust, and you curl into a ball and build a moat or a wall around your wounded feelings. You learn to steal yourself against the pain, convinced, never again, then you breathe, learn and understand scar tissue gained though painful lessons is priceless, once embraced.
That's just one dimension of being on your own. There's being far away, everyday, reality raining down, little time to find answers, right or wrong, something has to be done. So, you just do, have to make do, make the best of it, live with it, deal with the consequences. Maybe, ultimately, it's when you lose a parent, recognizing, maybe for the first time, the cushion and continuity they provided and just how deeply you loved them and the void they leave behind. Whenever and for whatever reason, slowly, whomever willing, you understand this is it, nothing more, nothing less, just this. You're on your own!