We, we cannot have that, you must be happy, happy.
So, here is how to keep you both happy:
In Rio, and many Brazilian cities there are restaurants, mostly lunch places, called Comida a Quilo, which are cafeteria-style places where you make your choices, load your place, and pay by weight. Some of them have very good vegan options as well as carnivorous and dairy options too.

So, the first one was the one that started that option in Rio and is one of my personal favourites. in fact, I'll be going there after this post. That is Couve Flor. It is very good, and has a very loyal clientele which includes meat, sushi, vegan and vegetarian. Every day there's tofu, in at least a couple varieties.
It is open every day for lunch 11:45 to 16:00.

Next is one that has an unlimited fixed price buffet and is exceptional. There are now three of these in Rio de Janeiro, all three in shopping centres. Rascal is the name. There are lots of options here too.

Third is one that is famous among the upscale and society-conscious types who populate Rua Dias Ferreira in Leblon. It is Celeiro, another food by weight place.

There are many other options but we'll make certain that you can indulge your carnivorous tendencies while your companion can be gentler to the state of the planet.