Welcome to the board! You should find much benefit here. Becoming involved in polyamory can be a lonely place, since it's still a rare relationship style in our culture and has been for several thousand years, in Western culture at least.
When I was newly starting to put my toes in the poly waters back in 1999, I also wondered what I was getting out of it after a short infatuation phase. New relationship energy (NRE) is a powerful drug. If you've been mono a long time, it can be very exciting, extremely exciting, sexually. You got sexual gratification from "hot wifing..." The idea of your wife having sex with another man, and having her tell you about the sex, can be a lot of fun for some men. You didn't have NRE for another person, you had NRE for the situation. And your wife seemed like a new woman, and hotter to you, since you knew another man had been sexually enjoying her. It gave you a new perspective on her. Sort of a voyeuristic thrill.
Now your NRE for hot wifing has faded. Your wife has established a relationship with the other guy, and having her tell you about it has started to make you feel loss... which can cause jealousy, loneliness. My example: When my ex husband and I started poly, we were unicorn hunters. I was bi and we'd been mono 20 years, but suddenly he decided my bisexuality meant he could get a threeway, possibly. We found a woman, and she indicated she wanted both of us, but soon it became apparent she was only interested in him. I had no time or energy for seeking another partner (either male or female) and suddenly we were in a mono/poly situation. I wondered, well! What am I getting out of this now? Less time with my husband. And he was less available for the children, home care, pet care, car maintenance etc etc.
I went from feeling excited I was going to get to be with a woman, to feeling like my husband's mom, getting the house ready for the gf to come visit, or helping him pack to go off to her place for the weekend. Not fun at all. Long story short, we ended all that, we divorced, and later he ended up with her.
But since my divorce, I've been with a poly partner. A woman. We are both poly, we both have bfs. We've been together 9 years.
But I can still answer your question. Even if I am "getting my jollies" with my bf, I do have benefits from my gf having one of her own. More time to myself. Knowing she is being appreciated and loved! I know how lovable she is, and enjoy knowing someone else sees what I see. Plus, we are both bi so i know she gets benefits from a male, things I can't provide.
But we do poly right. We talk constantly, kiss hug cuddle have sex. Date each other. Share projects. Travel. Cook. Share TV shows and movies, talk about them. Read books and talk about them. Do home projects and crafts. Talk about news, current events, politics, our friends and families. We are very tight. We are interdependent, though, not codependent. We both have hobbies of our own, and platonic friends of our own. We take vacations and trips together sometimes, and other times alone, to see our families or friends.
It's important to keep it all in balance. I hear that you're no longer getting the same gratification you got out of it originally. But of course, it wouldn't be fair to your wife or her OSO to veto it now. That would just be selfish. Could even ultimately lead to divorce.
I think you continue with therapy and self growth so you can altruistically enjoy your wife's happiness. And hopefully you can move from codependence to interdepedence. It's good you're aware of being too tightly enmeshed. Our culture encourages and almost demands romantic partners be each others' "everything." But actually, that is not really very healthy. There are a lot of great people out there. Why spend all your free time with just one of them?