How do you know when someone wants you to leave them alone?

Is it when they leave you?
Is it when they let you leave?
Is it when they never speak to you?
Is it when they never speak of you?
Is it when it seems like you never existed to them, and that everything that happened was just a short dream?

And lastly, how do you know when someone hates you?

I’d love to know what to do when you’re dying to say something, say anything, to them.

Do you keep your mouth shut and hope they have forgotten?
Or do you try to reach them and pray that they still feel something?