Hello PolyMC! I am also in upstate NY (waves!!). Welcome to Polyworld!
I will share some of my own experience with you, as there are some similarities between what you are dealing with and what I have had going on in my life.
I was already poly when I met my husband, now married almost 18 years. I made it clear to him (I thought) that I was poly, and while I was willing to be mono for a time for us to establish our own relationship ( I was inclined to do that myself, not just his request), after a couple of years and one kid I was ready for more.
He has always had trouble "sharing". Not just me, he has trouble sharing things like ice cream too. Childhood stuff, Im sure. But as I am bisexual, I agreed for years to pursue only women and not men. This was easier for him to deal with, and it is likely because of the no PIV potential...
This past winter, I reconnected with my high school sweetie and BFF. It was instantaneous, our chemistry has always been high together, and the few times we have seen each other over the years has always been something we both looked forward to intensely. I was his first love.
This was the "dealbreaker" relationship for my hubby and I. When I realized this was happening, we had to deal with the fact that I was going to be in relationship with another man. Which was very hard for him. Plus, there was an element of "there is no choice here, I am doing this." Which was very hard for me to say to him, and we spent many hours talking it out, crying it out, and my BF was very patient and understanding about it all. I realized that he was also my first love, and we have always loved each other, and always will. It is a lifelong connection that neither of us will walk away from.
What I have tried to explain to my husband is that, the whole point of poly (for me anyway) is that I can have them both. Or more. He sometimes gets caught up in the "you will like him better" or "he will do XXX better than I do, and you will want to be with him" mentality. Which is a mono thinking, that I would choose one over the other. I CANNOT choose one over the other. I LOVE them both. As hard as things are, I do not want to leave my husband. I love him and our family. What I DO want, is for BF to be part of our family. Someday maybe that will happen. But, what hubby is still learning is that I dont have to leave him to enjoy my other partner. We still share our connection. What it isnt, is exclusive. That's all.
We also did the "No PIV sex" for a while. We held out for 8 months. Which was really really hard. I was "done" waiting for him long before that, but we did not have the opportunity to be together all summer because of kids and other family stuff. Now that we are over that hurdle, we are now getting down to the real work of poly, the acceptance of the reality of this lifestyle, all the ups and downs, and all the joys as well. And my husband is learning that I can be with someone else I love, and have a sexual relationship with him, and I will still come home and snuggle with him, have sex with him, and have our family.
My advice to you would be to take it slow, and talk a lot. If you and T are okay with keeping things the way you describe for a while, then that may be a gentler transition for you all. But know that it may become hard to stop yourselves after a while. And, it should be your decision what you do in your relationships. Having your spouse enforce "rules" about what you can and cannot do with someone else, when he is not even around, is controlling. It may make him feel safe in the short run, but the sooner you can get past that the more genuine your interactions will be with both men.
Good luck to you!