Since you were born into the pure blood greengrass you were held to a standard since you were born. Your mom made a contract with Draco's dad when you were 2, stating that once me and his son, draco are 18 we must get married. Obviously there are rules to that contract like: No divorce, must have at least one child in the future, we must live together, etc. It's 6 months before my 18th birthday when i was told about this arrangement. You don't get along with draco very well either.