Host (2012)

After an experimental mind swapping procedure goes awry Avery finds that her once terminally ill husband, Dean, is no longer quite the person he used to be. His new body is perfectly healthy but in his mind lurks something dangerous; someone else. Now free, Harvey is hungry to have his own life back and he will do anything to keep it. Avery is forced to either let Dean continue living a half life, or to finally accept his mortality and allow herself to move on, freeing them both from the invader in their home.