guy friend stopped talking to me?

Ive first met him a few months ago, Im 14 and he's 3 yrs older than me. He treats me like his little sister but sometimes people ask if we were dating or something like that. We don't have any romantic feelings, I've even mentioned while texting him that I wont date him cuz he's like my best friend since I was worried that the rumors would ruin our friendship. When we're hanging with a group of friends, he would walk by my side or sit by me on the bus and always ask me if I was okay. When he found out a had a fever without telling him, he got really protective and told me I can always tell him if I'm having any problems.He walks me home if it's late at night.I told him I don't have anyone to talk to, he told me he cares about me and he'll be there for me. But recently when we met, he didn't talk to me but he walked up and talked to others and I felt like he's avoiding me a bit. But at the end of the day, as he was about to leave, he patted my head and ask me to join him. But since then. He stopped talking to me and ignores me. Ive even asked him why he was mad at me but never returned my text messages.Why did he treat me differently, I don't know if I did anything wrong or annoyed him.What should I do?