Well, not cheating, since it's all known about and consensual, and for the photos, I was second-guessing myself so I went to check and it's actually only on the cuck route that happens, not the sharing route...
The "starting without him" is mostly when he's not far away (so once, she is behind a photo screen with the other guy, and the husband is on the other side, then comes to join once they get started; once they are moving house and the husband goes out to the car for another box and they start up in the couple of minutes he's gone; the one with the biggest gap is when they go to the other guy's house for dinner, separately, and she gets there first and they start up before the husband arrives). There may be a couple of other examples that someone with a fresher memory can fill in.