Gabe was perpetually getting into expensive trouble and then letting others bail him out.

But that didn't stop her from coming up with the money to pay for a lawyer -- even though it was entirely Gabe's fault they were arrested for racking up several speeding tickets and then doing backwards doughnuts in a parking lot in Idaho. After all, he didn't have the cash to pay his way out of the situation.

Anyway, she figured he was good for it. He emphatically promised to pay it back. And hadn't they talked many times about marriage, a family, the whole damn thing? She figured, "What's mine is yours."

Cut to a year later. Gabe and Margo have split up, not very amicably, and moved apart, but she's still footing the bill for what turned into a very expensive road trip. And she wants her money back: "What's mine is mine!"

As anyone with relationship experience knows, Margo's dilemma is more common than not. Just about everyone has a story about an ex who owes them money -- whether for a loan or rent, or in a grayer area, i.e. a shared weekend getaway or front-row tickets to that Blue Man Group show. It seems some people see the end of a relationship as a chance to wipe the slate clean -- of debts as well as emotional and physical involvement.

This can be particularly galling if the dumper is the debtor. Then, the one owed is stuck in a precarious position -- he or she might not want to appear petty by asking for the cash, and any contact with the ex is only going to add to the emotional discomfort.

Conversely, if the dumper is the one owed, he or she may choose to ignore the debt by way of apology. After all, who wants to be the one who says, "Sorry, I've started seeing your best friend, it's over between us. Can you pay me back that $500 for our weekend in Vermont?"

The fact is, though, some people will do to former lovers what they would never think of doing to friends. For some, it seems that damaged bank statements are just part of the old equation, "all's-fair-in-love-and-war."

"It's hard to see how that could be," says Samuel Black, an associate professor of philosophy at Simon Fraser University. His courses include a broad range of ethics-related courses.

"There are many different kinds of situations. But if you make a promise to someone that is a non-monetary promise -- let's say, that the kids will be read to a certain amount each day -- even if the relationship falls apart there's no reason to think promissory obligations are no longer binding. If that's true, the same principle could be applied to monetary relationships. It's hard to see why the simple fact two people have had a falling out would extinguish obligations that have been voluntarily incurred."