I'm very sorry to hear about your situation; it certainly sounds very frustrating and difficult for both of you. Have you given any thought to seeing a relationship therapist? Given your history with your current wife, and given your previous relationship difficulties related to your SF, it might be worth it to get some help with sorting out your feelings about your SF, with identifying all of the barriers to maximizing your mutual happiness and satisfaction with your wife, and with communicating with each other to work towards eliminating these barriers.
While it might seem like you're out of options at this point, there might yet be alternatives to explore that you can't yet see because you're simply too close to the situation.
I hope that you are at least avoiding the temptation to beat yourself up over having a SF. Again, as I'm sure you realize, and as I hope you're reminding yourself, you obviously didn't ask to have the sexual feeling about smoking that you do!