I may have a backwards view on this but sometimes you just need to put your foot down instead of waiting and hoping that she'll have the decency to respect you and stop her behavior. Right now she is getting her cake and eating it too (so why worry about the consequences of her behavior if there are none?).

She gets to run back to you when she wants and she has the safety net of a "marriage" (and I use air quotes because at this moment it doesn't sound like one really... imo that is) that will still be there when this thing looses it's excitement or the chick leaves her, and she gets the excitement and thrill of having a new toy on the side (since we don't really know how she feels about the other woman - or at least I don't remember reading you describe anything more than lust atm... sorry if I'm assuming).

In my relationship with my wife (we've been together for 12 years and married for 2) we've had to put our foot down with each other more than once. Earlier in our relationship her anxiety got so bad that she wouldn't even leave the house... like NEVER! Not for doc appts, not for school which she eventually dropped out mid semester, not for family/friends events, grocery shopping, nothing! I was fine with her not working as long as she kept up the house but even then her fear/anxiety was soooo bad that she wouldn't leave the bedroom all day. At first I was fine with this but in the end it got to me and as much as I hated to do it, I told her she had to get help or I was leaving her because I couldn't live like that. I told her I loved her and I'd stand by her every step of the way but I couldn't live like that anymore. I felt like an *** for putting her in that situation but she did it. She got herself to the doctor and we got through it together. Now we go everywhere and have so much fun together... she's done a 180 and she's so much happier, thus our life/marriage is better for it.

Another time, about 6 years ago before I was diagnosed with bipolar I was in the middle of a really bad manic episode and she had to do the same thing to me. She said I see a doctor for my erratic behavior or she was going to leave me. I had to decide what was more important, my relationship or the manic high. I agreed to see a doctor but god did I resent and hate her. I almost thought about leaving her. But if it wasn't for that slap in the face and the fear of the consequences (ie her leaving) I honestly wouldn't have changed.

During our time together I have brought up the idea of polygamy and multiple lovers (I have a high sex drive and she doesn't) and we have talked about it in length. But I think (and this is only my opinion) that this all should have been worked out and talked about before she cheated, and straight up, that's what she did... she cheated. She did not have your blessing or permission to start seeing other women at the time, thus she was unfaithful to you and your marriage. I believe that, and like I said I may be old fashion in this regards, but in a marriage you BOTH should be happy and you BOTH should be able to trust the other. If you BOTH can accept the other going out with other people but returning home at night, then go for it! But if it's hurting you this much then it's not a good marriage and she has no right to treat you the way she is. You should feel loved, safe, and respected in a marriage and atm you sound like you're experiencing none of that. She's only caring about her pleasure and her excitement and she honestly doesn't care about you or your feelings, and that's why she is forcing you to accept her decision by making you cry and not giving a **** about your feelings because she knows what she's doing is wrong but if she get's your "Permission" (however she can get it) it makes everything all right in her mind.

But anyways, just my two cents. I'm sorry it got so long... I just feel for you so much and if you need someone to talk to please feel free to hit me up in a private message and we can talk about it some more... if nothing else I can listen. Best of luck to you both.