One of the odd cruelties of heartbreak is how much useless knowledge it leaves behind. Their coffee order. Which side of the bed. The exact face they made at a bad joke. Nowhere on earth to put any of it.
That information fades on its own schedule, unevenly, and mostly while you are busy with something else. You do not decide it out. You simply find, at some point, that a song came on in a shop and you got as far as the second chorus before noticing.
Nobody can tell you when. Only that it does thin, and that missing someone is a different thing from being unable to go on without them.