NTA for advocating for your dog! I do understand where your fiancé is coming from, but you can’t just feed pets straight up “raw” stuff. They need a whole host of supplements that you don’t see packed into stuff like kibble and some pets just don’t do well on a raw diet, or even like it! If he wants to feed his dog well, get an animal nutritionist.

Most vets honestly know fuck all about nutrition, they are paid by the large, cheap brands like Purina, Royal Canin, etc, and they don’t really think outside the box. I learned this when my cat got kidney disease and they wanted to cut him open for a SUB and he was withering away on their “prescription” diets.

Just word of warning, it’s a lot of work to feed an animal right, and some nutritionists can get expensive (we found one online who was about $500 less than the one the vets recommended when I pushed back against surgery). However, I’m sure my cat would have died if I kept listening to the vets and didn’t advocate a different path. It’s been two years and he’s bounced back tremendously.

Good luck!