“It's impossible [to get off car leases],” said Blake, 33, who ended an engagement with her fiance. “You have to refinance, and it would have cost us $14,000 to get off each other's [car] leases. We stayed on and luckily, we're not the kind of people who who default on things. But a few months ago I paid one day after the “suggested due date” and I was freaking out—What if I get a late statement? What if he gets a late statement? I love this car, but I swear, I'm going to have a party when I turn it in, because until then—on paper—I am still bound to him. Being on a car lease is more binding than marriage.”

Sign on the dotted line

No one dreams of an anniversary filled with roses and contracts. It's not romantic, but a cohabitation agreement now prevents a Wapner-style he said/she said smackdown later. That said, this should be a joint undertaking, something the two of you hash out together. Springing legal papers on someone is jarring, and talking through these issues is a chance for both of you to express desires and concerns and even get to know each other better.

The agreement doesn't need to be complicated. In fact, the simpler the better. Make sure it's clear that both people will leave with all the personal property they brought, and specify who gets the house, the dog, etc. If you have lots of complicating factors—kids, large debts or assets—make separate contracts for each issue, rather than trying to create one giant document. And if anything is confusing, get help from a lawyer.

While decisions themselves may be complex, composing the document is easy. You can find forms online, but there's no harm in drawing one up yourself. Nothing is iron-clad, but most small claims courts will uphold any document they believe was signed in good faith—even if it's crayon on a placemat.

But whatever issue the agreement hashes out or how it's composed, don't mention—or even allude to—sex. Courts get touchy when you use language that might be seen as legitimizing prostitution, and if your contract states that you pay the electric bill and he flips your switch a minimum of three times a week, a judge is likely to toss the whole thing out. One couple had their case tossed out because they referred to each other as “lovers.” It's best to keep non-monetary agreements—how many nights his drunk best friend can crash on your couch, who scrubs the toilet—out of it as well.

Unfortunately, there's bad news for residents of Illinois, Georgia and Louisiana: In those states, living together is still considered “immoral” and because of that, a couple can't create a contract defining the terms. Things may be getting better in Illinois, though, since one court decided that contracts that don't resemble marriage claims and aren't based solely on living together can be enforced. So if you're trying to do this in The Prairie State, see a lawyer. If you're trying to do this in Georgia or Louisiana, well, you might as well give it a go, since laws could change before it becomes an issue, but know that the document may not hold up in court.

A word about common-law marriages