Everyone of you has a Life Force that flows through you, connecting you to everyone and everything around you. It also connects you to the greater pool of Energy that we all exist in. That life force flows around you and through you, it makes your heart beat and your Love swim.
The Western world adopted the simple scientific term energy for what the ancients have always known to exist. For them, the proof was to look around and open their hearts to what was and still is.
Christians think of this energy as the Holy Trinity, the Jewish faith calls it Ruach Hakkodesh. In Asia it is referred to as Chi, Ki or Qi. What you call it is less important than acknowledging that it exists and that it creates what we think of as the thread between the physical and the spiritual worlds. By whatever term you use, it is the life force that flows through all things, creating an existential link through time and space connecting everyone and everything together.
Einstein famously stated that energy can never be created nor destroyed, it can only change form, and this is what happens when someone passes on from the physical to the metaphysical. Where they go is so far beyond our comprehension that it is not even worth trying to figure it out. All we need to know is that they go somewhere and rest in the space of not knowing.
Think in terms of conduits of energy where the sea, the land, even the air you breathe are channels through which the endless cycle of energy flows.The same holds for you. In the larger scheme of things the sights you see, the scents you smell, the sensations of touch are simply energy that your eyes, nose, mouth and fingers are energy that your brain files and stores, and when someone passes from this world the energy of their love remain forever. It is up to you to recognize their energy and to hold onto the memories that are their spirit. Every time you think of them or dream of them you bring them back by connecting to their energy. In effect, you have the power to keep them alive simply by remembering them.
Do so when you feel lost or in need. Do so when you miss them and want their warmth to surround you. Do so and you will know that they are alive and well in whatever form their energy has moved on to. And know that they are still a very real part of you and of the existence we are all a part of.
Be well and I hope this helps.