Everyone has one: the city they didn't move to, the person they didn't stay with, the offer they turned down out of fear dressed up as practicality. Somewhere there's a version of you who said yes instead of no, and that version has a whole life you'll never see the inside of — different apartment, different accent maybe, a different face across the breakfast table.
You can't know if that life is better. That's the part that actually keeps you up — not the loss of the life itself, but the not-knowing, permanently, on purpose, because you can only ever live one line of the story.
Who is that other you? Be specific. Give them a job, a street, a Tuesday morning. Then notice what it feels like to let them go — not because they were wrong, but because you're not them, and you never will be, and that's the whole deal with choosing anything.