What is my character's reason for doing this?

hmmm, well they he can be chasing her because maybe, her father abondened his father and now he's after revenge becuase his father never got over her, or maybe, they're betrothed and lets say shes like a specific race of people, or has a speical ability that he hates and "would not lower himself" t breeding with her so he has top kill her before the deadline of their marriege. Maybe even, hes chasing after her because shes part of a legend that is coming to fruition soon and know one knows the consequences so hes out to kill her out of fear of what to happen but they end up falling in love.... thats some of my ideas