Correct me if I got this wrong...you fall for this women, she gets her husband to agree to open up the marriage. You then try to get your wife on board, with the help of the other couple she comes around...You and the women are HAPPY for a time. Then because of the circumstance and now relate-able the situation, the husband and your wife form a support group which leads to them becoming involved with each other. That made you (unhappy). Its a struggle for you with jealousy and the usual stuff. Then she told you she loves you but not " in love" with you or see's you in a lustful way...or not turned on by you (from memory)....this was a crushing blow to you. The two of you then have problems sexually and things further devolve.
And now you have become so tortured by all this you want to stop.....and want her to stop as well. Or at least stop having sex with the other man or couple. Ideally you'd want it to go back to the way it was a year or 2 before you got that great idea.
Did I get this essentially right.
It sounds to me you carry a lot of guilt and other emotions for pushing this situation into 2-3 peoples lives and now you're the one that can't handle it.
Maybe you need to get some therapy or counseling to figure out what you really need or want independent of the group. However now that you put these other balls in play you might be screwed as to actually achieving it.