"It's inevitable, Damon." On this point, Luke would not budge. "She's your natural enemy. Do you think you can fight instinct forever? Furthermore, she's the enemy of all those you call, however loosely, friend. Were I to promise not to harm the girl, it would leave her no more safe. Not even you can protect her from the whole of our kind." He must realize this. How could he not?
In fact, there was only one thing he could do to ensure the girl did not suffer a fate similar to Roselyn's.
"If you're not willing to take the necessary precautions to ensure you don't lose her, you may as well distance yourself now."