Theory

So I have a theory.
When you love someone so much that they become your other half it's like they grab hold of a part of you. And when or if they leave they tear the part of you that they had a hold of, But you keep the part of them you held onto as well. And their part replaces the part that you're missing.
It's like when you have to get a replacement organ after your own fails. Your body never truly accepts the new organ because it's not your own but it eventually accepts it to the point it will use to it survive. And it may hurt for a while or continue to hurt mildly for a long time, but now it's part of you.
This happens every time. If you loose someone you love, a lover or a friend leaves, Eventually you'll have a whole bunch of parts of people you've loved. And you'll them as your own.
So that's my theory