Cohabitation is generally defined as two people living together as if a married couple. State laws vary in defining cohabitation. Some states have statutes which make cohabitation a criminal offense under adultery laws. Under one state's law, cohabitation means "regularly residing with an adult of the same or opposite sex, if the parties hold themselves out as a couple, and regardless of whether the relationship confers a financial benefit on the party receiving alimony. Proof of sexual relations is admissible but not required to prove cohabitation." Another state statute defines cohabitation as "the dwelling together continuously and habitually of a man and a woman who are in a private conjugal relationship not solemnized as a marriage according to law, or not necessarily meeting all the standards of a common-law marriage." Yet another state, Georgia, defines cohabitation as "dwelling together continuously and openly in a meretricious relationship with another person, regardless of the sex of the other person."
Living together, or cohabitation, in a non-marital relationship does not automatically entitle either party to acquire any rights in the property of the other party acquired during the period of cohabitation. However, adults who voluntarily live together and engage in sexual relations may enter into a contract to establish the respective rights and duties of the parties with respect to their earnings and the property acquired from their earnings during the nonmarital relationship. While parties to a nonmarital cohabitation agreement cannot lawfully contract to pay for the performance of sexual services, they may agree to pool their earnings and hold all property acquired during the relationship separately, jointly or to be governed by community property laws. They may also agree to pool only part of their earnings and property, form a partnership or joint venture or joint enterprise, or hold property as joint tenants or tenants in common, or agree to any other arrangement.
Other legal issues that may be affect cohabiting couples inlude estate planning and medical care. Generally, someone who cohabits with another is not considered an heir under the law or have the same rights to make medical care decisions in the same manner as a spouse. Therefore, unmarried cohabitants may consider estate planning and power of attorneys in addition to having a nonmarital agreement.
In some cases of people who formerly cohabited, courts have found a trust created in property of one person who cohabits with another, whereby the property is deemed held for the benefit of their domestic partner. When there is no formal trust agreement, a resulting trust may still be found under certain circumstances in order to enforce agreements regarding the property and income of domestic partners. If there is evidence that the parties intended to create a trust, but the formalities of a trust are lacking, the court may declare a resulting trust exists. The court may also declare that a constructive trust exists, which is essentially a legal fiction designed to avoid injustice and prevent giving an unfair advantage to one of the parties. This may be based on the contributions made by one partner to the property of the other. Each case is decided on its own facts, taking all circumstances into consideration.
A minority of states have anti-cohabitation laws on their books, although they are largely not enforced. State laws also exist allowing cohabitation as affirmative defense in certain criminal sexual offenses. Cohabitation alone may not qualify as common law marriage. Under the terms of an alimony order, payments may cease if the recipient cohabits with another. Some state statutes and case law allow modification or termination of alimony based upon a significant change of circumstances, such as cohabitation. State laws involving cohabitation vary by state, so local laws should be consulted for requirements and applicablilty in your area.