Vis a vis the movie, I think, if there is a film you really want to watch with your wife, you need to tell her so. I'm assuming that she didn't know that it was important to you for her to watch that movie with you?
Are you getting enough social life together as a couple? Maybe you could schedule a regular coed movie night that you could both participate in? Or join a movie group on meetup.com together?
Vis a vis the threesome, she jumped the gun before you two had figured out your rules of engagement. But it sounds like you did both agree to have an open relationship, just hadn't formally agreed to a start time. While I don't think her behavior was cheating per se, she absolutely should have checked in with you before she did anything sexual with your friends. It's good that she told you about it afterwards, and it's good that you still trust her.
This would be a good opportunity to let her know that you do not like surprises, and that transparency about each other's intentions and activities is important to you. One of your ground rules for an open relationship could be that neither of you proceeds in an unplanned sexual experience with a new partner or partners, without a quick check-in with each other.
Please don't brood over being left out of the threesome. If you are interested in group sex, I guarantee that there will be other opportunities for such, even if your best friend's wife isn't interested in a repeat experience.
Last edited by scarletzinnia; 12-23-2013 at 09:25 PM.