Here is what I was thinking about the whole thing. I don't blame the swinging. I don't agree with the swinging because if you're going to do that, you shouldn't be married in the first place.
I find it interesting that Tom and Trina are the happiest couple. They are the ones who suppress nothing and the ones who are open and honest. I know there was that thing with Bobbi, but it worked out because of the relationship.
Bruce and Susan and Roger and Janet had problems boiling over underneath the surface, and the swinging simply opened the door. I think I explained this better below.