Why has my guy friend been kind of ignoring me?

Hi, I had a guy friend in school, he was one of my best friends actually, and we have been really strong friends for two years. We used to hang out together with our other friends and joke and play fight kind of thing. I don't know what it is but he has been kind of ignoring me for a while. It's not like a phase like 2 weeks or so, it has been around 6 months. I don't know if it is because we moved schools or what but I am really confused. You see, when we first moved school we were still really close. We had an opportunity to pick lab partners and he picked me all the time. At this time i sort of developed a crush over him but he didn't know. And I swear that I didn't tell anybody about this. After about 3 months of our new school our friendship sort of downgraded. He found new friends and starting to hang out with this other girl, which many people say, looks and acts exactly like me. Come to think of it we are almost like twins, exept she puts on quite a lot of make up, I don't mean like a little she looks like a cake face(sorry for being rude.) I noticed after a while she was flirting with him. Every girl notices when a girl flirts because she was hugging him, ruffling his hair and all sorts. He looked really uncomfortable though. When she hugged him, he backs away after a second. Soon he hardly even talked to me. I was lucky enough to get a sentence every two weeks. They started calling eachother best friends and all that. The strange thing is though, when the girl went away for a month he started to joke around and talk to me every day. I felt great but it was really strange. I have also been ill a lot, in and out of school all the time and back and forth to the hospital. He dosen't even turn around to look at me when I laugh anymore. The other week though we were watching a video in school and he was saying all these jokes and that and my friend noticed that he looked at me about 4 times to see if I was laughing, I am really confused thx for listening x :