getting over a crush

there's this one boy at my school who i had a crush on for a couple months. before summer started i told him how i felt and he said that he didn't feel the same way. of course i felt bad, i mean, no one likes getting rejected, but i completely understood. we are still friends, but it's slowly killing me just being friends. and now that school has started i have more classes with him and i see him a lot more. you'd think having the whole summer to get over him i'd moved on by now, nope. in fact, the feelings are even stronger. someone please, how do you get over someone that obviously doesn't like you back?