Possession
(2009)

Roman (Lee Pace) is not actually possessed by Ryan, his brother and Jess’ husband. 

He got intimate information about Ryan and Jess by reading old love letters of Ryan to Jess and stalking them from time to time. 

Jess (Sarah Michelle Gellar) found out about this and confronted Roman. 

They got into a fight and Jess killed him in the end.”

Thanks Emmy!