sometimes part of loving someone is letting them have what is best for them, and respecting their decisions. it sounds like right now, her decision is her husband. both she and your wife sound amazingly understanding, and I'm glad that the communication thus far has been so open and honest...that's a wonderful friendship and you are very lucky.
the first thing you need to do is let her (the other wife) know that you want to give her and her husband a little space over the next couple weeks, but that you're not letting her off the hook as friends.
a couple weeks without constant contact will give both of you perspective, and help both her husband and your wife to feel more comfortable. after the two weeks are up...ease back into the friendship, but start off by only having contact as a group...not one on one unless she initiates.
during the two weeks you need to sincerely do your best to separate your feelings for her from your dissatisfaction with your marriage. In other words...if you had never met her, would you still feel the need to leave your wife? how long have you been dissastisfied with the marriage, and what exactly are the issues? are they issues that you and your wife can talk about? try your best to entirely leave the other woman out of this...i know they are intertwined feelings, but you will regret it if you leave your wife for another relationship that wont work out. if your wife and you need to serparate, it needs to be on the merits of the relationship between you, not based on a fantasy that simply cannot happen.
after spending some time gathering your thoughts, i would be open with your wife about what you've discovered, and ask her to join you in counseling. having a third person's perspective will give you a clearer view of what your main issues are, and what needs to be done. try to find a counselor who is understanding of the lifestyle, so that your activities outside your "marriage bed" aren't misunderstood. seriously give that a shot.
best of luck....