Draco Malfoy - The Unbreakable Vow

When Draco Malfoy becomes a death eater he Is set to complete a task, in his sixth year at hogwarts, set by the Dark lord himself. In the summer when he became a death eater his parents set an arranged marriage for the Malfoy's and Greengrass' to join families in the christmas break. Draco and Astoria fall madly in love and promised to never leave each other, Bellatrix being Bellatrix suggests they make an unbreakable vow. They both believe they wouldn't leave each other so they made the unbreakable vow. Will he regret that decision when he catches feelings for Kate. Will he stay with Astoria or be happy with Kate?