Why does this guy act differently every time I see him?

Anonymous
So this guy is 21 and I'm 16. yeah I know, he's a creep, I'm stupid. yeah so what, we're not dating.

Earlier when I knew him, I'd basically be a sarcastic bitch. He'd fall up the stairs and I'd be like oh nice move, he'd hit is arm on the door and I'd make a smartass remark.

Later I realized what a bitch I seemed like, so I tried being extra nice the next time I saw him. That's when he started acting like an ass. Now he turned the tables and he's saying all these little comments. And when I got his number and we texted each other one night, he didn't answer me until about a week later randomly saying "can we consummate" The next time I saw him he just acted really awkward and weird. I just don't know what to think because he acts different every time I see him. So since new years is coming up and he's probably going to be at this party I'm going to I don't know if I should just back off.
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finishing what I was typing to zuvgwyx, the 21 year old friend won't even talk to a 18 year old he likes because he thinks he's a creep or something. I've known him for probably 5 or 6 years, I don't see him that often though, like once or twice a month.
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he actually is my best friends, older brothers, friend. yeah its kind of messed up. and she like her older brothers best friend. we hang out with them on the weekends when they're at her house. He's actually chillier when all of the guys are there, if him
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and just a couple other friends are there, he's all awkward. when the whole gangs there, he doesn't mind talking to me instead of them.

&& don't worry about that, I'm not that kind of girl.
Why does this guy act differently every time I see him?
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