What happens to Victor Frankenstein's family early in his life that forces Victor to become more of a loner?

The monster that he had created killed his younger brother William, also leading to the false accusation of their adopted daughter Justine Moritz. These events causes Victor to be a loner, staying in the mountains.

Explanation:

In the story of "Frankenstein" by Mary Shelley, the main protagonist is Victor Frankenstein who was a young scientist. In his zeal to learn of the mechanics of life, he created a monster, who he immediately repulsed. This made the monster angry with his own creator. In his anger, he killed Victor's younger brother William, and the community had put the blame on a young girl named Justine Moritz, whom the Frankenstein family had adopted. Justine was eventually convicted and executed. This caused immense grief to Victor, who knows that the real killer was his created being. But unable to reveal it to the world, he began to distance himself from the others and went to stay in the mountains.

Though they Frankensteins had always been a happy family, due to his creation, Victor feels he had brought this disaster on his family. He blamed himself over the incidents and decided to be alone, away from everyone so that he will not drive the monster hurt them any longer. The death of the two individuals he loved led to Victor becoming a loner.