I do not think this is due to Bipolar, but more of a preference/obsession to watch movies.
I've known a lot of people that will watch a movie over a few times, and they were not DXed with any disorders.
Yearly when certain movies are aired on TV, people will watch them over again. When there are marathons of certain movies or TV shows people will religiously watch them even though they have seen them.
I wouldn't get too upset with his movie watching, but try to have a talk with him about doing something different once in awhile.
Because he has a DX, try not to read into every thing,this just may be his personal character/personality.
I know it can be easy for one to feel that way once a person has been given a DX.
Does he take meds and sees a pdoc, periodically?
Med a pdoc appt compliancy can mean a world of difference, making life easier for him and you.
Please take care now,
DE