Sometimes we want some people in our life until​ the end of time. But that feeling may not be from both sides. They may not be ardent, they may not be there tomorrow like they're at present. With time, they'll slowly and nicely avoid you. And you'll feel ignored and isolated very soon. You will miss them, thier presence, the memories, everything related to them. This causes pain. But this is not at all your fault. If they don't wish to be with you then simply leave them. If it's easy for them to forget you, you're also brave enough to reciprocate. Let them go. You just don't let the pain occupy your life all the time.