Welcome to the forum! And thank you for taking the time to write out such a long post. I know those always take a lot of time and energy. I have to admit, I had to read your post twice because there were things that I got confused about. There are a few things I wanted to say though.
1. You talked about how her swinging evolved into...
And your kink became...
But then you say...
Perhaps you two aren't clear about what each of you defines swinging, hotwife, and mild cuckold. Is it the case that you liked having her go out by herself but you still wanted to do couple swapping occasionally?
2. Your swinging days are not over once you hit over 30 or after you have kids. The majority of swingers are over 40 or 50 and can swing because their children are moved out or old enough to take care of themselves during the night when the parents go out for a date night. And there are couples who do swing when they have younger children. It might not be often but it is the occasional treat to do so.
3. You said:
But on the same note:
I bolded the last sentence because it sounds like you're pretty convinced that you talked her into swinging. If you're convinced this is the case, then why do you have so much anger and resentment when all the arrows point toward you that you may have created this problem of your wife not being 100% on board with swinging from the first place?
4. People change. I hate to be the messenger of bad news but people change all the time because we're experiencing new situations and ideas constantly. People can change for the better or for the worse. People can change to be smarter or dumber. People can become enlightened or not. Perhaps your wife has decided that instead of seeking other men out to play with and then those encounters becoming an emotional affair, she has decided not to go down that road. Perhaps she had a bad encounter and doesn't want to do any swinging. Or perhaps she wants to place her interest in something else right now...like motherhood and the arrival of your baby.
5. Instead of leaving the door open to swinging, perhaps you should try taking swinging off the table completely and focus on being a family. Leaving it open might make her feel pressured to try to do something swinging-related for you. Since she is your wife, she probably knows how obsessed you are about swinging and if it's the go-to thing to try to make you happy, then she'll keep half-trying to make you happy.
As I was going through your post for a 3rd time, I realized that it doesn't matter what confusion I had from your post. The bottom line is that whether or not she enjoyed it or not in the past, she isn't interested right now. If she's not interested, you need to drop it. If you can't and all you can think of is your desires and wants...not your wife's or upcoming baby's arrival, then perhaps this is a hurdle that you can't overcome. You are putting yourself first, not your wife, not your baby, and not your relationship. All you can think of how you want to swing, how you feel that you are missing out on swinging during your "prime", and I can sense this extreme build-up of resentment that you are holding against her. Yes, maybe she enjoyed it. Or, maybe she didn't. What ever may be the case, she has decided to focus her interest elsewhere. If swinging is in the future, then it will be. But if it's not, then you have to decide whether you will be okay with that or not. If not, then I don't think this relationship is going to work out without some major change in perspective in what is important. I'm usually not this blunt about this sort of thing but the combination of how you feel an urgency to swing, a resentment of not being able to swing, and this overall "me me me" in your post leads me to believe that maybe your wife picked up on this. All of this interest and obsession with swinging and sex takes a lot of energy...energy that might be taken away from putting effort into the relationship with your wife. And perhaps this is why she ended up having emotional affairs.
If you feel that exploring your sexuality and engaging in non-monogamy is pivotal in your well-being and you can't be with someone who differs with you on that point, then you should have your answer. You have to make that decision on what is important, who is important, and what compromises you are willing to make.
But please, take my advice with a grain of salt. This is the internet. I don't know you or your wife. We only have your side of the story. A lot of what you wrote concerning your wife's thoughts are speculation. I know you wrote that the two of you have talked a lot about this but perhaps not everyone was being honest or non-judgmental. I felt that there was a lot of "I think my wife feels..." in your post. Perhaps instead of only thinking...perhaps you can get into the realm of knowing how your wife thinks and feels about all of this.
Good luck.