"Is this what others expect from secondary relationships, to have growing intimacy, emotionally and physically, without growing emotions?"
No. Frankly, I think he's being willfully obtuse, or else just very dense. This has happened over and over, and yet he insists he's being the sensible one? No. Emotions happen, and they're normal, natural, and healthy.
A secondary relationship simply means one in which you are close and yet are not building a life together. It's about the degree of involvement. Any conditions you add after that are simply baggage that the term doesn't, in itself, imply. If you want that baggage, then cool, own it. But don't pretend it just comes with the territory, because it doesn't have to Iit doesn't in my secondary relationship with my married gf!). Maybe you two can never become involved to the degree that he and his wife are involved in each others day to day lives, but that's no reason to have to limit your feelings for each other. Two people can be deeply in love and yet not share their lives on a day to day basis. What is he afraid of?
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.