Disclaimer: Rowling? Yes. JK! Shoutout to my homegirl Sarah :)
Severus Snape is a bright child, at age five, and he decides the word Muggle means violence. He sees his mother cowering, hand pressed to cheek, and hates his father with a passion. (He hates his last name more.)
He never asks, but he's always wondered what made his mother leave her family for him. He's heard of the thing they call love and doesn't understand it, but he does understand that he'll never fall into it. Certainly the mysterious love could not be behind Eileen Prince's actions. Only the weak fall in love, he thinks, and silently vows to remain strong. (Everything changes when he meets Lily.)
He meets his second hate on the train to Hogwarts. He'd never considered the spells he knew dark, merely defence or even protection (Tobias Snape, after all, was not an easy man to live with) but suddenly dark looks good when it comes to James Potter. It is, after all, what Potter is always hissing about Snape anyway. The world of power beckons, tempting with the promise of showing arrogant toerags like Potter their place.
His love for the dark arts almost (almost, but never) exceeds his love for Lily, but she doesn't understand (how could she) and in the end it is one which drives away the other.
Years later, in his nightmares, a voice taunts him. He's not sure whose. It whispers, "How does it feel? What is it like, knowing that YOU killed Lily, that it's your fault she's dead, she's gone, she's not coming back?" He hates the voice and Voldemort and Dumbledore and even Lily, for dying to save James Potter's son. (But most of all, he hates himself.)
When he next sees the child, the one with the eyes he loves and the face he hates, he doesn't understand why all he feels is empty.