Some traditions never leave the wizarding world. But really, arranged marriages? What is this, the 1800s?
[Disclaimer, this takes place in the late 1990s for easier writing.]
Pureblood familes just can't let go of status no matter what type. First born son isn't an Auror or Curse breaker? Disowned. Daughter isn't an Alchemist or Healer? Disowned.
Nowadays, pureblood families have a strategy to keep relevancy. Remember the lovely first born son? Marry him to the successful pureblood girl down the street. How about the beautiful daughter? Marry her to your buddy's promising son.
Seriously, how can they accept muggles and mudbloods and not the fact that children grow up in different ways?
It's all silly, really, but lookie here. You are now in this unfortunate situation!
Congradolences.
As of the summer before your sixth year at Hogwarts, your family made this decision of theirs known to you. Unlike most cases, its because you were so quiet and shy, they thought you could use more lively company.
They chose Sebastian as your future husband. The description of a charming trouble maker was too familiar.
Word got around quickly, too quickly, even after he was advised by his friend, Ominis, to keep quiet for a while. As you walked into the Transfiguration Courtyard for some alone time, you heard that irritating voice accompanied with that familiar dark aura.
"There's my fiancee!" He called out to you, his entourage of friends snickering to themselves. You did notice he was proudly wearing his engagement ring, though you doubt it was by choice.
The worst part is, you don't even like the guy.
And your family told you last minute he's a vampire. Great.