Not even with your wife.
Ok, maybe your wife. But NOT your girlfriend of two weeks. She's going to dump you soon anyway.
I'm not linking this to add fuel to fire Silvermoon drama. But I did find the entire incident an outstanding reminder of why people shouldn't share their accounts with anyone and why people shouldn't assume that because someone says they're quitting for good, that they actually mean that.
I lay blame at both parties involved. If you give your account info to a friend, you almost have to assume that your username and password won't stop with that person. Don't want someone messing around with your toons while you're vacationing from Azeroth? Then don't share account information! And if you're playing on someone's account, you almost have to assume that the original owner will someday show up and want it back. Yes, even if they said six months ago that they were done with WoW forever and forever and forever.
I myself alternate between playing and quitting WoW. My most recent break was just last month, after some solid months of raiding. At the time, I felt exhausted with every aspect of the game; the prospect of months more weekly raiding made my head spin. But then a month away from it and I suddenly had the urge to play again. I've experienced this cycle before with WoW and I anticipate that I'll experience it again. I tell people, "Yeah, I think I'm done with WoW," and they roll their eyes at me and say a knowing "uh huh" and when I reappear weeks later, they show little surprise and only give me a little grief, which I have coming.
Which brings me back to people playing on accounts belonging to people that have "quit." Just know, they'll likely come back. And when they do, if they inherit a ton of loot and gold that you slaved on for months, don't be shocked or pissed, don't assume they're going to analyze the gold and gear on the toons and hand you a cut. Just grin and bear it because they should have never shared the account with you, you never should have been playing that account to begin with, and even if you didn't deserve to have all that work go to someone else, everyone definitely should have known better.