Ok so I'm in middle school, so we went to p.e, and I was just standing there, waiting for my class to start. Then all of a sudden, my close guy friend( I'm friends with all the guys over there) puts his arm around me, looks into my eyes and says" I love you" I couldn't believe what he just said, so all I could answer with was 'what' half smiling( I like him) then he said he was" joking"(hes done this now like 3 or 4 times to me and only me, he's never said that too any other girl, I mean besides his Ex, who dated like two years ago)

In middle school it can mean anything, from he really likes you, to it was a dare from his friends, to he was just joking around.

He is the only one that knows what he means, and if you are really friends, you sit down with him and ask him

I agree with fr_chuck. Since he said joking it could be really a joke or he just chickened out. If he's really close then ask him.