I've seen a quote from somewhere that goes like this. "If you never heard from your debtors again, then it is worth it." I know it is poignant to lose that amount of money and over a friendship that was probably built from years of spending time together to boot. But in retrospect, one can only accept the truth and move on. Or if you're really bitter about the whole ordeal you can always sue him, you found a way to at least see that he's living a pretty affluent life, you could find out where he is and send him a subpoena. Blue pill or Red pill bro, you choose.
I guess that is "Buda way", things happen for a reason, and we need to accept them and move on. I would probably choose that way, I would accept "my" mistake, and I would let it go... but it's me. I know people who would act in totally opposite ways, even with less money at stake.
OP is probably making peace with this situation by posting this stuff online, it's probably a relief when you share your burden with others. People of action wouldn't waste time on that... that's for sure!
A friend should never be treated that way, no matter how much money is at stake. You lose a little bit of your faith on humanity when friends turn their backs on you. Money shouldnt be the most important thing in your life; it should be secondary to love and friendship. But really, after something like this, you can only move on and try to avoid making the same mistakes. You can't let people get under your skin and hurt you.