Man o man this is fraught with potential problems. If you are not present how are you going to stop the green monster from imagining all sorts of things; and why the hell does she not want you there? How do you feel about this; the way you have written it doesn't instill confidence that your emotions have been considered and that you are, in fact, surplus to requirements?
We suggest you need to have a very full and frank conversation with your wife as to why she wants this, and more importantly why, at best you are only being offered a bit part, so to speak. This seems very one sided, and as such, unhealthy.
Perhaps suggest she goes to bingo whilst you shag the daylights out of a couple of 18 year old vixens; would she be happy with that?