All the harry potter fans out there.this ones for you.?

Snape's mom is supposed to have tolerated an abusive marriage with a muggle inspite of being a possibly slytherin pureblood and a competent witch(seeing that Snape's excellent).why do you think it was so?in the sixth book the half blood prince's potions book was 50 years old .it was eileen prince's.but wasn't that the time voldemort was at hogwarts too?do you think he is Snape's dad?