Setting is smilar to van helsing and crimson peak.
A nerdy guy walks up to a castle and finds a girl wearing white. They fall in love and sleep together. The next day, they guys wakes up and finds that the girl has become really old and decrepid. He panics and runs down a tower/long staircase. Another guy,vampire like guy that loves/engaged to the girl, catches up and says that only he can really love the girl. The girl catches up, becomes heartbroken and say.. I thought you love me.
The girl and vampire-vibe guy disappears and the nerdy guy is left wondering