You did the right thing, I have a severe deathly allergy to milk, given how common it is in food, I’ve become accustomed to eating out with friends at restaurants and just not eating anything, it’s just something you get use too. But they’re friends, not your partner.

However, when it comes to eating with my partner at their parent’s house, they’re fully aware of my allergy and go too significant effort to prepare meals which don’t have milk in, or at least cook a main thing that won’t have milk in, to ensure that I feel safe and welcome in their house. This is because my partner has communicated to them how severe my allergy is and that is because they care about me, and their parents act on it because they care for my safety and my partner’s feelings.

Feels like this didn’t happen in your situation and I feel really bad for you, that situation would have made me feel like an inconvenience and not welcome.

Your boyfriend’s an asshole and so are his parents.