It depends on the people. To me, comparing it to a couple not agreeing on a vegetable is not at all the same as agreeing on whether or not to contribute to animal suffering or not lol. My husband and I both went vegan at the same time and I think he may have been far more angered by everything he learned from it. But then, the whole thing was news to him; I was used to it, sadly. Before going vegan, I was angered and sad by the whole thing, but I thought I needed meat for health, so I just avoided factory meat and went with nearby farmers. Still not ideal, but it was me or the animals at that point lol. Now we know better.. it's not us or the animals, we don't need to eat them to survive and we shouldn't either (just my opinion, of course).
Anyway.. I don't believe on forcing opinions or beliefs on others, but I couldn't be with someone who isn't vegan themselves. I'm with my husband for life, whether he starts eating meat again or not. If he does, he'll just have to keep it far from me. But if something were to happen to him and I found myself back out there again (fat chance lol), I would only date vegans, to make life simpler. I can't stand the industry and the suffering and I would feel awful seeing that across the table from me every day. To me, it's not a matter of being different and to each their own.. we're talking about cruelty and suffering. That's not just a food choice for me.