I am Jim.
My heart goes out to you for the feelings you are in the midst of. You're clearly in a big struggle. The way your husband has delivered this information bluntly (and probably without being completely forthright,) is hurtful.
It is very possible to love more than one person without loving either or any of the other partners any less, so when he claims his love for you isn't diminished that may be true. His actions, however, suggest carelessness with your feelings.
You stated there is no sex planned so far. I would recommend you brace yourself immediately. I suspect that even if it's true that there hasn't been sex, or been a plan for sex, there has certainly been desire and intent for sex.
It sounds to me as though you are being given information piece by piece in order to gauge your reaction before he proceeds. (i would hedge that he has proceeded further, but your tears halted his admissions.) I'm fairly confident he didn't intentionally hurt you. The problem is, he also didn't intentionally NOT hurt you. Therein lies the rub. His priorities and procedures are completely in disregard of you. Demand he take a break while you sort this out. Demand honesty going forward. Honesty must come beforehand, not confessions after the fact.
Also, I would wonder what his story is to his other partner. In Poly, at least here at my house, the stories all of you get should match nearly perfectly. If they don't it is a dead giveaway there is deliberate deception afoot.
I wish each of you all the best. Let the truth be your compass.