Hephaestus
Imagine, if you will, the god of craftsmen, Hephaestus, builds the world with each person as a wire. Alone, a single wire will bend at the slightest pressure, and two can hold twice as much, but still bend. Hephaestus saw this, and his heart heavied, how can love bring people together and hold up their own world if they bend so easily? He thickened the wires and again he found that they bend so easily he cursed and pounded his anvil hard with his hammer. He was angry, and being in his great forge only made it worse, so he decided to wander the Earth for a time. He ventured through forest and desert, mountain and valley, ocean and pond, but nothing helped soothe his rage within.
He seemed to lose all hope in forging humans to love with all they have, since it was not enough to hold anything. He put his hand on a tall tree, a tree that reached nearly to the foot of the heavens, and he asked it a simple question,"How can you, a giant of the ground, reach so high into the sky, and not break in heavy storms? How can you do this for so long and not fall to the ground that nurtured you when you were but a small seedling, fragile and searching for your place?"
The tree gently swayed in the afternoon breeze, and a branch the size of a normal tree, bent and gestured for Hephaestus to put his head on the loamy soil at its base. Hephaestus sighed and rested his head on the ground. He pulled out his two wires from his pocket in his apron, and rolled them between his fingers. He had his eyes closed and pondered how such a complex problem could ever have fallen into his hands. He laid there for some great time, with the sun high in the afternoon sky.
He opened his eyes to the brightness of the sun piercing his eyelids and peered upward to the tallest tip of the tree. Shocked, he bolted upright and stood to investigate what he saw. He pushed his face flush to the trunk of the tree and looked upward once again. He could not believe how simply the tree had answered his questions. Hundreds of years ago, it had already found the answer. He laughed wildly as he took a tool from his apron and held the wire ends within it. He then began to twist the two wires together from tip to tip, intertwined from beginning to end. This new twisted wire was stronger than he could imagine, holding hundreds of times it's previous limits with ease.
So to answer this question of why love hurts when lost is as simple as pulling one wire from this creation. twisted and weak, the remaining wire is even more vulnerable to bending that before it was twisted together with the other one. Losing that other wire can make life seem that much harder than before, because each point was twisted and formed with both together, and without the other holding it in place, all of the pressure bends that what was once hundreds of times stronger than it could ever believe. Losing that love that twisted two people together is worse than anyone could ever imagine, and that is why love is so powerful.