I find your fiance's behavior here kinda worrying. It seems callous, or at least... lazy?... for him to allow this relationship to continue when he doesn't even want to be touched by her, and to refuse to try to identify or talk about the problem. If I were you I might tell him that seeing him treat a partner that way is disappointing, and would make me wonder if he'd ever treat me that way.
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.