Lies are no way to start a new, unchartered path. Honesty is the only way to build a good foundation. . . your wife may need sex counseling. Some people have sex issues that make them act out. And if this is the case she needs a therapist to help her with that LONG before you can begin considering a poly relationship.
Yes it makes for great sex and then you feel guilty for getting turned on by the thing that hurt you the most. That's why there is a way to live to live this way and mind blowing sex together - most of the time - but you have to go back and start over with a clean slate and she really needs to learn a lesson on being honest.