They were. Damon was going to fuck Stefan. The brothers were going to have sex and Elena found it incredibly hot. She had to bite her hand to stop herself from making a noise when Stefan bent over the bed for Damon and started to tease his entrance.
Elena knew it was incredibly wrong to stay and watch but she couldn't help herself. The sight of the brothers together was just to erotic not to watch. Her panties were completely wet and Elena's free hand moved to one of her breasts, squeezing it through her shirt.