There are a lot of great points here, and if both parties are happy and comfortable in the relationship then I think that's all that matters.
I got very lucky with my boyfriend.
We were both meat eaters when we met, but both had open minds and an interest in learning about these issues.
We watched videos together and shared info we'd read, and made the transition to veganism together.
This made things really easy for us - we were already living together and sharing our finances, which is where I see a problem occurring in long-term couples with different ethics. I guess you could go your whole life keeping your money separate, but it would still be complicated deciding how to split the grocery shopping, etc.
Another difficulty would be choosing how to raise any future kids, which has already been mentioned.
I personally don't think I could handle the emotions that would come with seeing a dead chicken in my fridge, or constantly having to bite my tongue about something so important to me.
Of course, I'm not in that situation, so I can't say for sure what I would do, and I don't judge people who choose to date meat eaters - in fact, I think it would take a lot of compassion and selflessness to make things comfortable between you.
But here are a few thoughts I have from reading the comments above:
The general consensus seems to be that if your partner doesn't ask / want to know about this stuff, then you shouldn't tell them for fear of sounding preachy and scaring them off the idea.
I think if it was me, I would wonder why my partner didn't ask/care/want to learn about my reasons for making a choice that is such a big part of my life...
Using the example of religion above, I am not religious myself, but I have a couple of close friends who are deeply religious, who I am happy to talk about religion with, and I frequently ask questions about their beliefs and practices. It interests me because it makes up such a big part of who they are, and although I don't believe in the same things, I still open myself up to hearing them, because my friends obviously care about it a lot.
With veganism, I think "don't ask, don't tell" is generally a pretty good way of avoiding sounding preachy to casual friends and acquaintances, but I don't think the same should apply to a partner who you are supposed to be able to share everything with.
Having said that, it would bother me more if my partner DID know my reasons but still chose to contribute to the torture of animals. Ignorance is excusable, but once you KNOW better, I don't see any excuse not to DO better. (except taste preferences, which is not good enough for me, if we're talking about someone who I would choose to spend my life with.)
Although I used the example of religion before, I do think it's important to recognise that there is a difference between respecting someone's religious beliefs (and other differences of opinion) and accepting someone's harmful behaviour.
Generally speaking, an individual's religious beliefs do not cause harm to others (obviously not including extreme cases like suicide bombers, funeral picketers or hateful street preachers.) There is no reason not to accept a person's differing beliefs or choices when they only affect that person.
We like to think we consider the lives of all animals equally... But would you be comfortable dating someone who frequently paid people to torture and violently murder fellow humans (usually children and newborn babies) for your partner's own enjoyment? I certainly wouldn't, and I would speak up about it if they didn't fully realise what they were doing. If they DID know the harm they were causing, I could not respect their decision even if I tried.
Lastly, I do think it's great if the person is eating less meat because of you, either because you cook for them or because you don't allow meat in the house. But if they don't share your beliefs, I can see that potentially backfiring.
Chances are some of your partner's friends/colleagues are going to learn that you're veg, either through food functions or just by talking to your partner.
Imagine how it would look from an outsider's perspective if your partner is going to work and stuffing their face with meat because they can't do it at home, especially if it's because of a 'no meat in the house' rule... People already have the impression that veg*ns are extreme without adding "controlling partner's food choices" to the equation. If your partner doesn't understand the reasons why you make those choices, it would be easy to simplify it and say something like, "yeah, she gets really upset if there's meat around" or "she's just really sensitive about that stuff" without having the ability to expand on it.
Of course, it might never come up, but if it does, you may be turning more people off than the one you are converting.
So that's a few things to think about, but like I said, this inner conflict is something I've never experienced myself. I have no idea what would have happened if I was single when I became vegan, or was in a relationship with someone who I already loved dearly who did not share my compassion for other creatures. You guys have my utmost respect for staying level headed in such a tricky situation.