It’s the same for us. Well, an average marriage is way less to me than my commitment, it’s for life. We could get married but it’s just a paper to me and I skipped it.
And it doesn’t matter anyway, maybe even 2 friends living together would be a tad similar: acceptance of the other person is very important even if it makes cooking for two more difficult. The same for someone living with their not small kid.
And I doubt a vow has anything about sacrificing ourself for the other… Standing by them, fine but giving up our very personal needs…? Sounds wrong, if there are such vows, I don’t want them.
And actual marriages… People often don’t even love and respect each other, well that’s bad.
I see absolutely no addiction here, in general. A high-carb diet may be perfect for someone, without any problem… If someone has a harmful diet or other habit, yes, it’s understandable that its close family member tries to change it but it’s still up to the one in question as we probably almost all know…
I don’t resist temptation but even I should be strong enough to resist carbs if I don’t want to eat them… And I am selfish, it’s normal but it would be a horrible selfishness from me to demand that my poor SO be on a (for him) unpleasant, restrictive style of eating. I couldn’t do it anyway, people don’t work like that.
But it’s fine if you both are okay with that. My SO and me completely agree regarding this topic, we aren’t self-ruining addicts and respect and love each other. Our circumstances are surely different so other things work for us. Even so, I don’t fully understand you. If someone is a true, weak addict, it’s still unfair to expect the other the sacrifice their own life while they did nothing wrong. If it’s not a sacrifice for them? Fine, we did that too. If it’s a tiny bit of a sacrifice but the one is willing to help the other, fine. But if they need very different things, that’s bad. I would search for some other solution. Many people don’t eat the other person’s trigger food when they are around. It may work in many cases.
It’s so good when we have the power to do things right, we aren’t puppets (or just puppets of our own desires but they can be changed. sometimes it’s hard and slow and almost impossible though), it’s up to us. It’s okay to be considerate, helpful to each other, we have that in this household. My favorite carby things (there are less and less) aren’t on the menu when I do keto because my SO is fine without them and I like to make my life easier. But I cook and bake carbs all the time because it’s needed, it’s normal for someone who cooks for a family… There are people better at it, like vegans cooking meat… I didn’t touch meat when I was a vegetarian but no one expected it from me. And my diet seriously affects my cooking especially the part which we both eat. But as long as others are fine with it, why not? 
But the main thing that different ways of eating shouldn’t come between family members. It never caused any problem with us, I just got stressed sometimes, making the same vegetarian food for a ketoer and a high-carber was a tad too challenging, no matter which of us made the cooking. But we did it and it could have been way harder or plain impossible, there was some common ground. And always will be. It would be a bit sad not eating the same ever but if that would be needed, that could work too.
