You'll start noticing things about them in a different way. Maybe you find yourself getting jealous when they talk about other people they might be interested in. You also might feel a flutter in your stomach when they touch you casually, like a hug or a pat on the back. And you'll find that you want to spend even more time with them than before.
Well, usually if you can access and view the content without any restrictions or prompts about it being private, chances are you're not on a private story.
Well, usually, if you can access and view the content, you might be on it. But sometimes there could be notifications or indicators specific to the platform telling you.