If they're people you still actually want to see how about compromising and just meet them for drinks after the film - will that leave you time to see Ben first? That's the part of the night where you will actually be spending time with them (as opposed to sitting next to them in the dark).
Ditto above. I never refused to go out with friends because of my horse. I just fitted it all in. I didn't see going out with friends once a week as an issue as I had 6 other nights to do more with my horse. I would just make a fleeting visit to the yard before I went out.