Well, first off poly to me (and most people) is about honesty and full disclosure. The description of it includes responsible and ethical non-monogamy. It is about integrity and consideration. The core root of poly is empathy/compassion. Cheating and having an affair with a man that is married and not up front with his wife, is not poly.
First off, I would suggest that he be up front with his wife and go from there. If he doesn't do this then I believe he should leave her. In order to live a life of integrity this is the only way I think.... I realize that there are circumstances that make this impossible, but I don't know what your's is and really. I am not easily convinced.
If you want to know why I am coming off as such a hard ass about this then please read some of the threads on this forum by doing a search in the search engine on "cheating" "affairs" and then read the "lessons learned" and "foundations" threads.... specifically this one
and this one
So lets say that you actually get through that... and you are where you are; I think you have A LOT to learn about poly and the basic concepts. All of you do. It is completely different than swinging and open relationships. Although there is a lot of sex by the very nature of the fact that many people are involved, the structure of is is based on healthy relationship dynamics. I don't see you as having that with your husband or your new lover. I would start with working on your marriage. I would leave the bf to get his work done on cheating and in the mean time work on this sexual issue you have. Every little thing that is a concern in your relationships will be blown up to huge proportions in poly dynamics... you might as well get on it while they are small and seem manageable before that time. Otherwise there will be chaos, pain and people could get hurt.... at least that has been my experience and that of many others that have come by this forum...