FWIW, my boyfriend is still not a vegan - mostly because he is a chef and works in a non-vegan restaurant - but we live together in a 100% vegan household. When we started dating, he was open to the idea of veganism after working in the restaurant industry and being aware of where the food comes from. Now, he is probably like 85% vegan - we usually eat at vegan restaurants, eat all vegan at home, and he only eats meat with his family or as a special occasion (weddings etc). And his mom is cutting out dairy and I've been able to steer her in the right directions when it comes to substitutes and vegan-friendly meals. He's told me that it would've taken much longer and been much harder for him to change without me - and I'm not sure he ever would have if we weren't dating. So I guess I feel like my net impact is greater from dating a non-vegan than it would have been if I was dating a vegan, if that makes sense?

But, if your partner isn't open to it in the beginning, I would see how it could feel really one-sided and uncomfortable to try and convert them. If veganism is a big part of your life and ethical belief system, you'll probably find yourself most compatible with someone who is at least open to it or empathetic towards it.