I was introduced to non-monogamy when Wife starting having a cyber-affair. When it was discovered, polyamory was proposed as a way of continuing the relationship. In hindsight, we both realize this was a huge mistake. (The affair ended shortly after that, and then we were able to START healing.) Polyamory requires a SOLID foundation of trust and (like many others have said), that would be VERY difficult considering all of them were willing and able to lie to you about the affair for quite a while before.
I'm on a Yahoo list for mono partners in a poly relationship and most of the introduction posts (including mine) read like your situation: Partner cheated, wanted to call it poly and continue the affair, and now I'm twisting my self in knots trying to cope. It's terribly sad.
I've read several resources about recovering from infidelity and nearly all of them strongly advocate that the affair has to end in order for any healing to occur. Using the "ballet" analogy, since you weren't allowed time or space to heal, the injury is still there. Worse, the "accidental drop" has been incorporated into the routine so it continues to re-occur, aggravating the injury. You CAN NOT heal this way, any more than you can heal a broken leg by jogging.
Ask your husband to google for a webpage called "Transitioning from cheating to polyamory". If he wants to save the marriage, that pages would be very useful for him. If he refuses, you should strongly consider the advice about moving on from a dead marriage.