Xander needed no one, least of all a mate. The woman was a menace to his solitude, calling to the Vampire within and daring him to take her. Instinct wouldn't allow him NOT to hunt her, especially with another male sniffing around what was his by right.
The female in Luna recognized her mate immediately, even if he was too much of a male to realize it himself. Knowing he would fight the attraction, she decided to wait and let Fate take its course. What is meant to be cannot be denied.
But in the end, leaving may be the only thing that will save the forever Luna feels in Xander's arms...