Often times it's best to be upfront. Tell her that you not only respect her boundary of your not having sex with another Woman but also that it is not something you intend to do at all anyway. Just tell her that all you wish is for her to reap the joys of being shared with other men, and perhaps Women too, if that's what she's into.
- There's no need to hide or pretend.
BTW it's great to know you are moving forward in this lifestyle. You and your Woman are going to have loads of sexy fun together, i'm sure.