Disclaimer: I own Harry Potter, if that doesn't sound legit it is probably because it is not true.
Summary: "Somewhat ironically, Snape is the catalyst for the entire series, since it was he who told Voldemort of the prophecy and begged Voldemort to spare Lily. Enabling her to sacrifice her life for Harry, thus enabling the protection that protected Harry for so long and ultimately led to Voldemort's death." Harry Potter Wiki.
It was 1955 when the ex-captain of the Gobstones team Eileen Prince became Eileen Snape against her father and mother wishes, labeling her as a blood traitor and forever condemning her son as the son of a blood traitor.
When Eileen went and started dating this muggle her father and mother warned her and threatened to cast her out of the family, forever burning her name and the name of her descendants off. After that threat they hoped that Eileen would come back to her senses and marry the pureblood wizard they chose for her.
Eileen paid them no heed, claiming to found love in the arms of the poor muggle worker and that this muggle loves her despite not being a girl of outstanding beauty.
That claimed love didn't push her to tell him about magic till later days before the actual wedding in the chapel.
Tobias didn't react… negatively, at first he was awed and loved seeing Eileen moving portraits and moving chocolate frogs and even eat the amazing Bertie Bott's Every Flavour Beans despite getting one vomit flavoured.
"I loved you when you were like me normal, and now that you are something else… I love you more." Was what he said while Eileen happily cried.
Eileen was happy and so was Tobias, they lived happily and carefree for a while.
A while that was three years.
In the fourth one Tobias managed to lose his job at the nearby factory and in turn forcing them to move into Spinner's End to save money, at the same time Tobias was slowly turning to a drunkard, cheating husband.
The first time Eileen caught him cheating, he started apologizing and promising to never do that again and Eileen forgave him.
That night was when Severus was conceived. Eileen hoped that with this baby Tobias will become better and stop drinking.
It was a cold January night filled with screams of anguish and pain, when a healthy but a tad underweight baby boy was born; Tobias was there and held the baby in his hand for a few minutes only to give him to his mother who decided on naming him Severus.
"My beautiful baby boy, my beautiful Severus." came the hushed and tired whispers from a woman who was deeply exhausted and on her way to deep sleep.
Despite being a quiet baby, Severus was already showing signs of accidental magic. Like having the bottle of milk move a bit towards him when hungry or the spoon filled with that yucky baby food fly across the room.
Eileen was delighted that her Severus was showing signs of being magical, Tobias was furious he didn't want any of that freaky stuff in his house, it is enough that he has to work now that Eileen will be staying home to raise their spawn.
By the age of five Severus was already used to his father filthy habits; he would drink beer and smoke while watching the telly… when he came home that is, whether from work or from a night out with his equally drunkard friends. Sometimes returning home eager to fight and hit his wife, careful to make sure that her Severus never notices anything, Eileen made sure to place a silencing charm around Severus room.
Severus was seven by then and quite aware of the tension between his parents and how sometimes his mother was covered in bruises. It was night when Severus came out of his room to drink water when he heard the sound of a slap echoing through the house followed by the muffled sound of sobbing.
Inching his way to see the source of these sounds, he found his mother huddled in a corner holding her left cheek, her lower bloodied lip already split and swollen in front of her what seems like a broken twig, after further inspection Severus recognized it as her wand. When Severus ran to help his mother, she snapped at him, telling – almost screaming – him to go to sleep, while his father was already in front of the telly losing himself to another pack of beer and the cigarettes between his fingers.
After then his mother seemed to stop caring, she stopped calling him her Severus, stopped telling him stories about her wizarding ancestry, in short she stopped caring just like his father did since Severus's birth.
That was when Severus began wearing mismatched clothes that after a while it looked deliberate; he also began spending as much time as possible outside their house, often found in hiding watching a little girl around his age that showed tendencies of what he and his mother could do. Magic.
It took little Severus another two years to actually pluck the courage to go talk to her, what helped him is seeing her sister calling her a freak for doing magic. From there Severus and Lily started forming a tentative relationship.
A/N: I had Eileen wand broken as I find it strange that a witch would simply give up to a muggle who most probably abused her and her son.