Missing someone is an agonizing feeling. You feel it with your whole body. Every part. The worst is the aching in your chest. That never-ending feeling. The feeling that you are missing something so important, like a lost appendage. And worrying about how you'll cope without that crucially important part of you. I suppose the only thing to do, if you cannot replace the person, is to fill the hollow emptiness that consumes you. To start again.