When Hestia first begged Zeus to make her a virgin, she did it out of desperation. Gods are eternal but their hearts, most of the time, are not.
Marriage benefits from, but does not require, love and respect; and so was Hera's complicated relationship with Zeus. She never laid with another, but faithfulness is a different story altogether.
Hestia didn't care for any of that. She didn't wish to be part of the drama; the heartbreak, the cheating, the jealousy. She preferred to be quietly in the background, tending the flame. So she begged for her life, and Zeus granted her request. No god touched her.
Then the world changed. Mortals, armed by the fire Prometheus had stolen for them, multiplied rapidly and evolved even quicker. Athena and Hephaustus aided them and they creates wonders previously unspoken of with every era. Many matched Daedalus's skill, and many attracted attention from the gods with their beauty.
Demigods swarmed the earth, tempting countless monsters from their chains underground. They tugged, and the chains snapped free and they, too, swarmed the land. Demigods died by thousands, and more monsters surged from the earth, hungry for the sliver of golden ichor flooding in the half-bloods' veins.
Hestia kept her head down. Sometimes she appeared in their dreams, gave them a word or two. Sometimes she burned goblets of nectar in her hearth and directed the smoke to other fireplaces, watched as wounds closed themselves on the wide-eyed demigods huddling for warmth. Sometimes she helped the mortals as well, staving off wild animals and diseases with her flames, and soon they learned to avoid them.
But mostly she fed the flames on her hearth and sighed at the horrible images flickering across the surface.
Then, a camp was made.
At first it was merely a restingplace for three demigods who had somehow found one another. They were covered in wounds and bruises, face and hair matted with dirt, limping and bleeding and exhausted. The first thing they did, after sticking wooden branches around them as a poor defence, was to build a bonfire. They burned monster fat and leaves and prayed fervently to the godly mothers and fathers they never knew, desperate yet hopeful in the way scared children are. Hestia came, and she blessed the area, and when they curled up near the fire - even the one who volunteered to take the first watch sound asleep - she appeared in their dreams as a voice and whispered to their subconscious.
(The bonefire stayed burning all night, warm and glowing.)
The next day when the three woke up, they created a simple sign and stuck it to the ground, with words scrawled in the red of crushed berries:
Camp Half-Blood.