I don't know what to do?

Okay so when I was in fifth grade my best friend moved to California. the summer after 7th grade I went to California to go visit her. The summer before our freshman year (last summer) she moved back. I was excited because we hadn't talked very much,we texted every once in a while. But when I came back from being at my dads for the summer she was there already and she came over quite a few times before school started. When school did start we met up at lunch everyday and even joined Volleyball. After about the first 6 weeks of school she was hanging out with a lot more people and had a lot of friends. It was cool she was making a lot of friends, plus she's very social. But then after a while we weren't talking as much and she never came over anymore. And I would even buy her lunch at school every day because she didn't have money to every day. And it's not like I had a lot of money either. We even had her birthdasy party at our house because her and her family asked and we were close so we said yes, that was in september. Point is we don't hang out anymore and whenI text her she never responds and I even passed by her in the hallways a couple times said hi and she didn't say anything back to me. Another one of my friends that we've known since elementary said she did the same thing to her and she is also very social. So I just don't know how or if I should confront her about it or just leave it alone. Any advice will be appreciated thank you:)