I have also become too afraid/tense/stressed to finish watching many movies. I never used to be like this!
I pre-record movies that look interesting then if the film starts to get tense I stop it and look the plot up on the internet (wiki) to find out how it ends. If the 'nice' people survive I'll continue to watch it. I think I just want happy endings now.
I also have noticed, since I turned 65 a few years ago, that it's very difficult for me to follow fast action in a film. It's another reason I record movies - so I can keep playing back the hard to follow bits.