Why is breaking up so hard to do?

There was something I read once (and I’ve looked because it was a lot prettier than my writing, but cant find it anywhere) that talked about how losing someone close to you is like losing a limb. You’re so used to that person being there, you automatically reach out to them. To call them when you’re happy or sad. To celebrate when you have good news, to hold you when you’re scared. And like the limb that is missing, you have to change a lot of things in your life. You have to let go of a lot of dreams and feelings that were associated with that person. And every time you automatically reach for them, you mourn the loss all over again. The good thing is, that you learn how to heal, you learn to adapt, and you no longer miss them as much after a while.

because you cared about that person so when you loose that person and dont have an imedeant replacment then you have a void