And there's a moral there somewhere.
Finding a (and or maintaining) a job in this economy is a pretty damn big gamble. Why do you go to Vegas and need money to throw away?
Unless your friend was feeling lucky and his gut instincts in that regard are pretty reliable, I'd say you were pretty . . . stupid for loaning the friend the money.
As for the other question (would I let it ruin a friendship), nope. Money comes and goes but friends (of the highest caliber) are priceless. Granted I'm pretty sure none of my friends would ever do that to me and at the very least I know they'd tell me"I'll pay you eventually" at the very least. . . .