There is nothing in the original post to suggest that the wife/girlfriend are bi and interested or into a BDSM dynamic. While it's a thought, triad experimentation can go completely haywire. I see a lot of people (not saying you in particular, since you seem to have a whole different dynamic going on) wanting to bring their original partners into their new relationship, because they want to share the excitement (when we are in love, we can't understand why someone wouldn't feel the same way about the object of our passions), because they think it will make the more reluctant original partner get on board with poly, or out of some misguided sense of fairness or coupledom (if I'm getting laid, so should they).
If the wife in question is mono, she will not be interested to seek additional sexual action for herself and will probably be turned off by the thought of her hubs being with someone else, as the OP seems to indicate.
Me: bi female in my twenties