I'm in exactly the same position as well.
The first thing I did was to cry - a lot. I just cried on my own in bed for a while and felt way better afterwards - once you acknowledge the feelings it's much easier to try and move on from them.
What I'm doing is just trying to accept that it's not going to be anything more than a friendship - and then appreciating it for the friendship that it is, and trying not to hope for anything in addition to that. The hardest part is not reading into his actions to see if there's anything more than friendship on his side - but if you are confident that he doesn't like you back, then you're already through with one of the hardest bits, as there's no false hope to battle.
What made me feel better is to consider how bad I'd feel if we weren't even friends. That was so good for me because it made me realise how lucky I was to have what we DO have anyway - so that way you can see the positives of the situation. At least he's your best friend - imagine if you'd never met him at all.
I also agree with the poster above me - friendship is far more likely to last and not turn sour than a relationship.
I'm trying to think like this with my friend - at least I'll still most likely be friends with him in 20 years, whereas I'd be unlikely to still be in a relationship with him in 20 years.
I hope you can begin to think this way too - but I understand how hard it is, and these past few months really have been awful for me at least. If you want to PM me about it I'd be very happy to lend a sympathetic ear if you need to talk to someone in the same situation :')
I hope it gets better for you.