First of all, the way you’re describing this ultimatum-type situation really won’t be helping anyone. You don’t force someone to do something by telling them they HAVE to do it or you’ll leave, it’s about education. My boyfriend is a meat-eater, but like the previous answer, eats significantly less meat than he did before we got together. He even went vegetarian for a few months and is planning on going back to it. How I did it? Nothing. I didn’t tell him he needed to, but more the fact he got used to being around that life style and adapted over time. At the end of the day, telling someone to do something will not necessarily get them to do it. If you’re so keen on the idea that you don’t want to be around someone who eats meat – maybe it’s time to rethink your relationship and look at the possibility that you’re saying this as a way of getting out of it. It’s his choice to eat meat as it is yours not to. You have to respect that as much as it morally and ethically goes against your own wishes.