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You have to be a little more forthcoming about this deal if you expect an honest answer or suggestions.
If you gave him $1,000 as a loan because he was short cash at that time, borrowed it from you with the full expectation it would be paid back with likely only minimal interest, then yes, he is screwing you by not paying it back. He's a loser.
If however, this was a business deal that you hoped would make a 20 or 30 percent return on that investment, and it went sour and you lost the $1,000, then that's just a bad deal. He lost. You lost. That's the way it is. If that were the case, I don't even understand why you'd expect the money back, and he might - and should - feel the same way.
If you "don't know the full details of what happened," and it was "never explained satisfactorily," that tells me you're just disappointed the $1,000 didn't turn into $5,000 or whatever like you'd hoped and you wanted to get out of it scot free - in other words, you wanted a risk-free investment, which as you know is not how the investment world works.
Without knowing all the information, it's impossible to pass judgment in any way. But you should take a harder look at the facts and see who the real aggreived party in this mess might actually be.
If you expected a return on your investment without any risk of losing your money, then that naivete tells me you might be on the wrong side...Or your friend did guarantee the loan, in which case he's the loser.