One night when Damon is sleeping she drives a stake through his heart.
Quite literally, of course, not metaphorically in the slightest. It doesn't entirely make sense but it's not as if she's never done it before. Maybe it's because she wants to see the look on her face when she comes around. Because she never stops coming. She will never leave them alone. She knows who Damon truly loves and it isn't her. It will never be her.
He will always be in love with her doppelganger.