Why is he acting this way?

So I like this guy and I thought he liked me back. He always sits next to me, agrees with me (Even if it means changing his opinion), tries to make me laugh and flirts with me. But then he was like "Are you nervous or something?" and I said "No." and he was like "Yes you are, why are you nervous? Your'e rambling and you're like nervous but what do you have to be nervous about?" and he was being kinda mean after that so I told him I was mad at him and he was like "Fine, have a nice day to you too!" and like got all mad. Then the next time I saw him (I didn't see him for a day cause i had a social studies thing) he was like "So how was the competition?" and i was like "Good, we won!" and he was like "That's awesome." and like went to hug me but stopped. Then he was like "Are you still mad?" and i was like "No." then he wa like "Oh. good ok." and looked all relieved. His friend has asked me if I liked him multiple times and when i bring it up to the guy he just blushes and looks away. I catch him staring at me like with a dazed/smiling expression when he thinks i'm not looking. Sometimes if i'm talking to other guys he gets jealous. But then the day before winter break he brought this present he was giving to this one girl to cl with him and some guy was like "Dude is that for your girlfriend?" and he was like "No, i wish." but then he looked at me and started laughing like i should have thought it was funny cause he stopped and kinda turned red when i didn't laugh. So then his friend was like "It's for (the girl's name) isn't it?" and he was like "Ya." and I was like "Is that why you redid the gift like five times?" and he nodded. So that was weird. But at this dance on New Years (i couldn't go) my friend walked by and said my name cause she was talking to someone else and he turned around and whispered something to his friend. Yesterday in cl we couldn't sit together but he kep trying to make me laugh and smiling at me from across the room. then today i get there and he's talking to this really slutty girl and then she walked away and he came over to me and told me he got like five detentions or something like that. so then like the rest of the time he was being really mean to me (telling me to shut up when i wasn't saying anything and telling me i talk to much) but being perfectly fine to the skank and this other girl in the cl with us. What is his problem? oh ya then i saw him in the hall and he was like staring at me (not angry but not smiling...kind of a half smile)