I think in reality though... You let this happen. I don't think this was her, though I don't know your relationship particulars, nor was I there. All I have to go on is what I read in your original post. I don't say that to be a dick either...just more to give you some outside insight that may allow you to have the sort of perspective to properly say goodbye to this relationship, and decide what you want from the next. Allow me to explain...
Mac is right in the sense that many who walk the razor's edge, end up in a similar place. When you read this forum, the majority of it is fake, made up, wishful thinking, active fantasy, etc... Guys that hope to one day be cuckolded come here, read a lot of this stuff and likely know a lot is fake, but it gives them great hopes that they too might one day be in a similar spot as many of the posters here. But again... most of it isn't reality. And for the few stories that are reality, there are dozens of bad endings that don't get talked about much because nobody wants to log on to the forum and read about how what they want so badly, can also end so badly. It's just not good for the buzz, so it generally gets overlooked and people become fixated on all the crazy things that are happening out there.
I think the people that manage to make this work successfully, long term, without damaging their relationship, do this together. It's about the two of them, not about one or the other of them. I think they spend a long time talking leading up to it happening, and then spend a lot of time talking and reconnecting when it is happening. By talking I mean more than a "you good?" and a "Yup I'm good" sort of talk. I think people review where they've been, how they feel about what's happening or where things are leading. I think people remain emotionally intimate and tight with one another along the way. Sure that doesn't sound like fun bed time sex chat...but it is required in my opinion if you're going to be successful and stay together. In your case the ante was constantly being upped, and from what you've written, the danger signs were running rampant, and you did nothing to say "hey wait a minute...I'm important here too, and this is about US, not just YOU." If you didn't say that at least once or twice along the way and stop all the action and put it in time out mode, to discuss how you both were going to get back on track with all of this together, then there's the issue right there. Why I largely exonerate your wife in this situation is because you let her do this, you ******* her to this, you told her you got off on it, she went and did it again and again, pushing the envelope, and you never once said no. What was she to think? She likely thought you were completely okay with everything going on, and even if she thought maybe you weren't, you likely said nah, it's alright, I'll be fine. When that happened, and the guy became the primary in your relationship, and they began to actually confide in each other, do relationship building things together outside of sex, that was the final warning that the train was way off course. But again, it sounds a little bit like you allowed that to just happen and did nothing to put your foot down and say "hey whoa now... this isn't going to a good place." You have to monitor these things...both by truly monitoring your wife's actions...as well as what she's feeling inside. Again, no sexually gratifying stuff, but important in relationship maintenance. The moment she was doing more fun things with him than you, and you sat back and failed to stand up and say enough, it's done, your relationship was doomed to end this way. She confided in him more at that point, had a greater excitement for him at that point, found him to be more than enough man at that point...and all the while slowly began to lose respect for you, and love for you. That's just what happens when men and women connect, and spend more time together in an intimate, dating style relationship than they do with their own partners. You ultimately being to look like just a means to an end...be it a half bill payer, or a roof over a head, a co-parent, etc... Your services are no longer truly required on any level. Sitting back you handed that all to her.
Now if at some point before this got to this point you had sat her down and said you'd no longer tolerate where this is going, and attempted to redirect things back to a couple's perspective... or if you had had long and detailed conversations all along, or if you had some rules in place to protect your relationship and make sure it always came first, or better still, used cuckolding to augment the relationship rather than to fantasize and ultimately replace it, I doubt you'd be in quite the same position you are in now. I genuinely think you likely played the biggest role in the relationship's fall.
Again I'm not trying to be harsh or bust your hump here (though I appreciate it likely sounds that way)... but if you want success (or at least the greatest chance at having relationship success in these circumstances), you have to be in it TOGETHER. You, and she (whoever the next she is) have to establish boundaries that protect your relationship in dangerous times, and as I so often preach...talk, talk, talk...oh and then talk some more. You can't just enjoy the ride and get off, and have no further real responsibility. The fantasy world people will pretend that's not true...but the reality is, it is true. It's a high stakes game with many outcomes that are hard to predict. But if you're not protecting what you cherish most, you're almost 100% certain to lose it.