Tonberry: I disagree that his wife being in love with the other guy is what hurts him. I think the lack of the full emotional commitment (committing all your emotional energy to one person) is what hurts him.
turtleHeart: You seem like a very mature individual, but I agree with Tonberry in the sense that I think you're not looking at yourself enough. Mono vs. Poly, as I've been exploring in my thread, is not about one or the other being correct. It's not that your wife shouldn't want anyone else, and it's not that you should be ok with your wife pursuing relationships with others.
Within the mature mono relationship it's well-acknowledged that love is not an exclusive feeling that you feel only for some magical one true love who shows up one day and everything is perfect. I don't think for a second that that's how you're looking at this which is why I don't think your wife loving someone other than you is what necessarily bothers you. It seems that what bothers you is that you've taken every available option to enjoy there being multiple relationships, but it doesn't work for you.
To be totally honest, I agree with Tonberry again in that your desire to be with your wife is likely coloring your answer. It seems likely to me that based on what you're saying here (and said in my other thread), your personal choice lies towards monogamy. You've obviously thought it out. You've tried dating other people. You've tried being accepting of your partner dating someone else. It's not some immature feeling of jealousy that has made you unhappy with that. You've tried dealing with every emotional and intellectual avenue to make sure that this is not just you being immature about something, and you're still unhappy.
I think you're a very mature individual. I think the amount of effort you've put into exploring this thoroughly and checking out every avenue is wonderful, but I think now it's time to consider yourself. You're considering your wife and the fact that she loves and wants to be with her boyfriend. I think that if you really examine this and decide that what you want (regardless of anyone else) is what comes with a monogamous relationship then you're going to need to sit down with your wife to communicate that. You have to find out how she feels about monogamy and if she would be genuinely happy in a monogamous relationship. It seems that you might only be genuinely happy in a monogamous relationship so if your wife would be genuinely happy either way then maybe monogamy could work for both of you.
If your wife would only be genuinely happy in poly and you would only be genuinely happy in mono then it may be time to face the tough decision. If that were the case, would it really be worth it for either of you to sacrifice your personal happiness to allow the relationship to continue? Even if one of you could sacrifice what would make you happy for the other (which it seems you're already doing), will that really result in the most fulfilling relationship that either of you could be in?
So my advice is make the personal decision about whether you're mono, poly, or some variant thereof as well as what you want from a relationship. One of the smartest pieces of advice I've seen is that being poly is not a couple decision. It's an individual one. Each individual has to decide what they want from a relationship and then a couple can potentially go from there. What's most important here then is that you and your wife both evaluate individually what you want from a relationship and then decide how you want to proceed.