I'm going to be blunt;

a.) your friend sounds like a bit of an ass...you may want to reconsider this 'friendship' if this is the sort of person he/she is.

b.) you don't seem to have come outright and let your friend know where you stand.

i don't care how good of friends you are, you are providing him with a service which you agreed he would pay for.

if he's not paying up, walk away!

next time, write up a contract. i just did a fairly decent sized project for a good friend, and he had NO issues with me producing a contract for the work, simply outlining how much he would pay me, and how much work i would provide for him in exchange.