It was the loss of his mother that set him out on his own. He didn't have a pack to call his own and had no one to rely on but himself. It wasn't a complete tragedy since he knew how to survive, at least physically. It was more that he had lost his one and only companion. Illness had taken his mother, something she had been fighting with for months, and hadn't been entirely unexpected. Ephy did what he could to help her but they both knew it was all for naught.
His mother encouraged him to seek out others, not wanting her only child to be all alone in the world. He made a promise that he would but he would not leave her side while she was still around. It was only after her passing that he thought to try and find a new companion.