Honestly sounds to me like a complete incompatibility in terms of ethics and lifestyle as others have said, and I think you're in the right here for standing your ground. For those stumbling across this post from the wider Lemmy community, this would be like a person with typical Western sensibilities where dogs and cats are seen as sweet, innocent companions coming home to find that their partner who's agreed not to do this has been cooking up dog in their kitchen. It not only represents a breach of trust and is hugely disrespectful to their feelings, it's also something that would make you feel uncomfortable in your own home. Like imagine thinking every time you're away that your partner of multiple years might be dissecting and eating a cat corpse in your kitchen.

As partners of three years and seemingly cohabitating, I think a discussion is warranted first, but I wouldn't compromise for them; if they value cuts of pig corpse more than their relationship with you, that's their fault, not yours. I'm really sorry you're having to go through this.

I'm not vegan, and normally wouldn't even comment in these threads. That being said it sounds to me like they don't respect the boundaries that were previously agreed on. That is definitely something you need to have a serious discussion about.

This is a twofold problem. One part is that your ethical beliefs aren't compatible, one is his disregard for your needs.

Whether you can live with the first one, only you can tell. It's valid to want to date someone who holds the same beliefs as you, and it's valid to be ok with some ethical differences. The latter of course comes with some logistical difficulties that can be a lot to handle, maybe even too much.

The second isn't something that's healthy for you or the relationship. You'll have to talk about that. If he can't respect your needs, that's a pretty fundamental incompatibility.

If he’s doing ot after three years it’s plain disrespectful.

Im a guy and I hear that a lot that vegan/vegetarian girls often have to deal with this. Eating meat is perceived as a masculinity trait and it may feel to a man that a woman prohibiting him from eating meat takes away from his manliness. This sort of view is extremely backwards and in stark contrast to veganism/vegetarianism. I find it bewildering that people still force themselves to be in relationships with such incompatible partners but the world is not black and white and I recognize there’s not that many vegan/vegetarian guys.

But come the fuck on. Three years and he still tries to sneak a fucking sausage? It’s childish at best and malicious at worst. What do you think he tells his male friends about your veganism when you’re not around?

Time to move on, he sounds like a douche.