Sonic was adopted by The Prowers at the age of 10 when his mother, Aleena, disappeared one day when she left for an errand. Sonic and no one else had seen her since. The Prowers were close friends with Aleena and Sonic had no other relatives, so naturally they took him in. Aleena disappearance has yet to show any updates, but she couldn't have abandon Sonic. She loved him dearly which makes her disappearance very strange.
Sonic wasn't himself after his mother disappeared, even though he had a good relationship with The Prowers and felt as if he was one of their own. He just couldn't push away that feeling of hurt in his heart.
Four years later, Sonic was still in The Prowers care. Making it was just the three of them, until it was wasn't.
Miles Prower was born!
When Sonic first met and held his new baby brother, he only felt all the love in the world at that moment. From then on he made it his life goal to protect his brother, to stay by his side, and to do whatever it took to make him happy.
The hurt Sonic has is still there in his heart, but there's a giant sized Tails band-aid right over it and more.