What should I do, im bummed about this...?

Okay so there this guy thats a sophomore, and im in 8th, well he told me last october that he liked me. anyways we've had this secret sort of relationship going on for the past 6 monthes, ish. well anyways im tired of this because he can hook up wth someone else, and vice versa. plus i dont like him as much, im more so crushing on a junior now. what do i tell him? im getting confused, he sends me mixed signals, like when anone else is around, in the room, he acts like we're just friends, but then when everyones gone, he just want to make out and such. this is starting to bother me cus i feellike im being used. any advice?