I fell in love with a human, and now my enemy angel is out for revenge.What should i do?!

Dustin is an angel who helps keep the peace on earth along with other angels. Dustin has mist(could make Dustin and the other angels; wings go in thier bodies)and would only show his wings when in battle with a demon or so.Dustin doesn't associate with humans often and only when it's necessary. But when a new girl named Serenity arrives to Destiny high school, he is intrigued by her. And shortly after her arriva, comes along Christian, an angel who is a follower of Saton(devil angel). Wanting to avenge his brother, he wants sweet revenge and will stop at nothing to hurt Dustin for he has killed his brother. And he might have foung it in Serenity.Dustin can't seem to leave Serenity alone, but he doesn't want harm to come to Serenity. Should he risk Serenity's safety and innocence,or should he complete;y forget her and leave her alone? What should he do?