My girlfriend (20f) and I (19f) have been together for almost 3 years. We both moved to another city for college and have been living together since.

We live in a big city, with lots of really great things to do. There is one thing in particular that I've been wanting to see forever, a museum. I've asked her multiple times if we could go, but every time her answer was that her brother (17m) also really wanted to go, so it wouldn't be nice to go without him. She told me that he'd come visit us and we'd go the three of us.

He came to visit us last weekend, but I left a few hours after he got there because I had a 2 weeks holiday and was going back to my hometown. Before he got there, I overheard her talking to her mother on the phone, and telling her that they were going to visit the museum. I was kind of surprised because she always told me that we'd go together, the three of us, so I assumed they wouldn't go when I wasn't there just like she didn't want to go with me without her brother.

I told her that it wasn't really nice of her because I'd been asking her to go for a long time and she decided to go with her brother without even telling me. She told me that they'd been talking about going together since they were children, while I'd only been talking about for a few years, but I can't help that I didn't know her back then, and I've literally been talking about it since the moment we got together. She also told me that she could go there twice and she could go back with me another time, but I told her that in that case she could've gone with me when I asked, and then again with her brother later.

It's not that big of a deal I do realize that, but it's not the first time she's done something like that and it kind of makes me feel unimportant in a way. I'm not saying what she did is awful or anything, but I just feel like it wasn't really nice to go without me when I've asked to go with her many times and she always told me we would. She doesn't understand why I'm upset about it and says that I should just be happy for her.

I've talked to some friends about it, just because I kind of felt like maybe I was overreacting and she was right but they all told me that they agreed that it wasn't a nice thing to do. I don't know if they just said that to be nice and agree with me or if they really mean it so I thought I'd get opinions from other people. So am I wrong for being upset?