I think the reason break-ups hurt so much is because you're letting a small piece of yourself starve to death.
Like, when you're single, you eat a little of everything and you're almost always full. Whether it's healthy or unhealthy you eat whatever you want, whenever you want. When you get into a relationship, you're only eating one thing all the time. Whether it's healthy or not, you now only have one source of nutrients. That's why when you miss that person when you're away from them. Because you're hungry. So naturally, when you break up, you're no longer getting that same nutrients that you were used to for so long. Sure, you could eat other things, but it's not the same nutrients. It's fast food. So rather than fill up on fast food, you have to let yourself starve to death.
Just a thought.