This post has what you might call a religious theme.
A person may refer to themselves as “Christian” or “Atheist” (or for that matter “Hindu” or “Buddhist” or as being a subject of one of several empires) however if the most important person to them is their false self-image (no matter how grandiose that may be), what they are actually doing in Real Life™ is Virtual Idolatry.
This is ‘virtual’ in the sense of there being no tangible evidence of the existence of the target of their affections, at all.
If you know of such a person, you will find dealing with their all-important false self to be very confusing, and sooner or later you will learn that to them your real value is zero. Nada. Squat. Nil. Nothing. Nix. You are (to them) temporary and disposable; the only limiting factor is that they will typically pull complex social manoeuvres to conceal their discarding of you, and/or portray it as apparently justifiable (or — more commonly — to be “your fault” and/or “unavoidable” as they Project their own inadequacies onto you).
The best general method for protecting yourself against being damaged by such a person is to quietly, tactfully, withdraw from their presence as much as is realistically possible.