There are many scenes which make it clear that in fact she is the victim. Theres a permament latent layer of meaning which shows that his only problem is her strange behaviour and not her suffering, he adressed that in many scenes. Even when she talks to him with clear mind in her sleep begging to just kill her all he answers is "is it so bad to be with me". Also when the one whish willow hotline askes if he wants to talk to the in the background crying and suffering " real nikki" he just denies. Pretty much every scene has these two layers: the classic horror where the crazy nikki hunts her victim and the layer of bear clearly knowing he just trapped this girl against her will for selfish reasons. It shows very subtle in the beginning of the movie and gets more obvious in the further course... I didnt recognize many of the more subtle signs in the first third of the movie until i saw it a second time, i can really recommend to do this (if you two find the time) and rewatch with another perspective, its very well done! Also after i saw it the second time i watched some analsysis and it showed even more details i didnt see the second time, i love how much love went into the details and the social relation between the four friends and what happens in the (sometimes blurred) background.