NO don't do it. No matter how much you think you have this great "friendship" I promise you, you will regret it. Never lend ANYONE money. I have never seen or heard of anyone getting their money back successfully and having them sign something doesn't mean a thing in SL. Bad, Bad BAD idea. So bad lol. Just BAD.
Walk away and if they give you the oh poor me bit, block them and move on.