Why did he just stop talking to me?

i was friends with this guy for a really long time and he would always flirt with me, but I never thought anything of it. Then all of a sudden he texted me and he asked me if I wanted to start talking to see if we have something. So we start talking and everythings going fine and then a couple days later he just stops texting me. The last time I heard from him was the night before when he said he was going to bed. I texted him but he never answered. I'm a little confused because we were talking normally and I didn't say anything that would've upset him cause he was fine the night before. The only thing I can think of is he's good friends with a girl that doesn't like me and she always starts rumours about me and he hung out with her soon after we started talking.