Black allows that complicating factors might come into account. When a relationship ends acrimoniously, someone feeling betrayed might believe that debts were accrued under false or misleading circumstances. "If the promise occurred because the person who received the promise lied to the other individual or mislead them, those are complications that might undermine the promissory obligation. But if there are no complications, I can't see how the fact the relationship has ended absolves people from monetary promises. I guess you could call me someone in the strict promise-keeping camp."

At a certain point, many of us might simply write off what we feel is owed, and simply chalk it up to, as one friend put it, "the cost of doing business." Obviously, you are not going to pursue someone to the ends of the earth for the cost of a frappuccino. But how about $250? Two thousand?

There is legal recourse in these situations. "If it's not common-law, the fact you were in a relationship is irrelevant," says Noah Neaman, a defense lawyer. "It's like any contract. If I agree to loan you $1,000 and you agree to pay me back, my recourse is to go to small claims court. Then it's just a matter of evidence, and whether a judge believes a contract or agreement took place."

But before you end up on People's Court, consider that it costs money to file a claim. "The judge may find there's uncertainty of terms, but that has nothing to do with the relationship. Generally, if I loan you money and you say I'll pay you back, a court -- if it believes there was a loan and an agreement -- will enforce it."

In that case, having something in writing helps but is not absolutely necessary.

Luckily, Margo, crafty as a fox, obtained Gabe's written admission of debt in several emails. To date, she's been paid back $500 of the $1,000-plus she figures she's owed. Although, she says, no amount can recompense for what she sees as two wasted years but that's another story.

Curiously, no one interviewed for this article admitted to being the person who welshed on a deal made in the heat of passion or even at the end of a particularly nice dinner. Perhaps, when relationships end, we're all under the illusion that we're owed something. Or that, in the final tally, everything balances out.