To be fair to him, if he is just filming rather than starring is there an issue? Or are we talking porn in the home movie just for kicks sense? It may just be me but he isn't actually being unfaithful or is it the fact that he lied to her that is the problem?
She doesn't know the full scope of his role - but he is definately organising the whole event. He had about 10 cv's from various models explaining what they were prepared to do and not do on the day and his responses to these.
The fact that he had explained he was going to visit his dear sick mother on Boxing Day and she had offered him the use of her car so he could travel around easier I think just compounds her sense of stupiidity. From what I understand some of the emails give details of events when he has previously said he has been at work (the proper job) etc.
Ahhh, see the lies would be the biggest problem with me. I don't tolerate it.
She needs to get rid and revenge, as you have said is pointless. Do be careful what you say though, because as we all know there is always a possibility she will get back together with him and then well, it's just awkward at best.
You have my sympathy, I hate dealing with the fall out from these sorts of things, I'm never too sure what way to play in it real life.