Why do guys get sick of their girlfriends?

My boyfriend broke up with me after 8 and a half months of dating. He was my first boyfriend and we never had any huge fights and then after a week of me being away at church camp I came back to find him saying he wanted to break up. He said that he's not ready for this serious of a relationship and that I was too clingy. (Which I wasn't) he also said that he didn't get to hang out with his friends enough, but it's not like he has to ask me permission to go out with his friends... I never held him back. I'm just confused. Why did he break up with me? is he just scared because we both want different things for the future? he's 18 and I'm 16.
Why do guys get sick of their girlfriends?
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