I'm sure you'll get your money...hopefully you have an email trail though where it's clearly stated that you're borrowing him $1,600 and he's to return it to you by such and such a time?
My girls and I pay for each other all the time though...if we go on vacay, usually we'll all call the travel agent to pay for our own portion of the trip, but there have been times where one person will foot the bill for the other, then the other pays them back. One time, the friend that was supposed to pay me back right away took it upon herself to pay me back in installments, which wasn't the deal, but whatever...she paid me back without a hassle...I just wouldn't do that again with her though cause when you're putting money out for someone, it should be on your terms, not theirs.