My Boyfriend’s Sister

A little back story: my bf and I have been together 4 years. His parents are living in Mexico and he lives with an aunt and uncle. I have never met his parents besides phone calls and FaceTime. He has three sisters younger sisters I’ve met like 2 years ago but briefly.

So his aunt and uncle he lives with decided to bring one of his sisters to live with them because she wants to go to college etc. We hung out for the first time this weekend, and it was very awkward and silent for much of the time. I tried making conversation and try to talk as much as I could without being annoying. There wasn’t a lot of talking from her part. The one thing that is bothering me is when we were going to eat dinner. I felt extremely uncomfortable. First in our culture it’s customary for the wives to serve their husbands. I don’t follow this “tradition” and neither does any of his family here. I saw she served his food and I was like ok whatever, but then he complained about how little he was served which kinda irked me and so I followed up by saying: well you can serve yourself more if that’s not enough for you, it’s no big deal if you serve yourself. Well….I said this and immediately his sister gave me a look like I was crazy..and I saw her and looked away and kept eating but in my peripheral I saw she was still looking at me and of course my bf was oblivious and didn’t see. And it made me feel super uncomfortable and aware that she is watching me and anything i do is going to be reported to my bfs parents.

I made the mistake of telling this to my bf and he got so angry he’s like she didn’t even look at you like that, you’re crazy, my sister would never do that. I was like you weren’t even looking. So immediately i saw that whatever I tell him he’s always going to take her side…and I told him that and he got super annoyed. I don’t even want to move out with him because I know he’s going to have her live with us along with his rest of his family. I don’t know how to bring up this stuff with him. He got so upset. He thinks his family is saints and angels and if I say anything he gets so upset. I didn’t say it in a rude way. How do I speak with him about this without making him upset. I’m upset because isn’t he supposed to believe me and be on my side?