If you aren’t married and neither is your partner, then no — adultery doesn’t apply to you in any legal sense. Every legal definition of adultery requires that at least one person involved be married to someone else. That does not mean an unmarried person in an affair is always in the clear, though. If the other person is married, or if you’re in the military, or if a court might treat your relationship as a common-law marriage, real legal consequences can still reach you.
What the Law Requires Before It’s Adultery
The Legal Information Institute at Cornell Law defines adultery as sexual intercourse between a married person and someone who is not their spouse.1Legal Information Institute. Adultery The married-person element is not optional. Every state statute and the federal military code carry the same requirement in some form.
Sex between two unmarried adults was historically called “fornication” and covered by separate statutes. Those laws are effectively unenforceable today and are legally distinct from adultery.
So if you and your partner are both single, the label doesn’t attach, no matter how serious the relationship or how hurt someone feels. If your partner is married to someone else, they have committed adultery. You have not — at least not by the strict legal definition. That distinction matters for criminal statutes, divorce filings, and military discipline. It does not, on its own, protect you from every legal consequence tied to the affair.
Are You Sure You’re Not Married?
Roughly ten states still recognize common-law marriage, which requires no ceremony, no license, and no officiant.2National Conference of State Legislatures. Common Law Marriage by State The requirements vary by state but generally involve living together, presenting yourselves publicly as a married couple, and intending to be married. Some states add age or duration thresholds.
If a court concludes your relationship met those requirements, you are married as a matter of law. Every adultery rule that applies to formally married couples applies to you. Divorce, property division, and any effect infidelity has on alimony all come with the marriage. Proving the marriage existed becomes the first fight, but once a court recognizes it, the rest follows.
This is the situation most likely to surprise someone who assumed they were legally single. If you live in a common-law state and have held yourselves out as married — shared last names, joint tax filings, referring to each other as husband or wife — check with a family law attorney before assuming adultery rules can’t touch you.
When the Other Person Is Married
This is where unmarried people run into the most exposure. You didn’t commit adultery, but in a small number of states, the wronged spouse can still sue you.
Criminal Conversation and Alienation of Affection
About half a dozen states still allow a spouse to sue a third party for damaging their marriage. Two claims are the most common. Criminal conversation, despite the name, is a civil lawsuit that lets a spouse sue someone for having a sexual relationship with their husband or wife.3Legal Information Institute. Criminal Conversation Tort Alienation of affection is broader and covers any conduct that destroyed the love and affection in the marriage, whether sex was involved or not.
Most states abolished these claims decades ago. In the states that kept them, verdicts can be enormous. Juries have awarded millions of dollars in combined compensatory and punitive damages. If your partner’s spouse lives in one of those states, your legal exposure is real regardless of whether your own conduct meets the definition of adultery.
Being Dragged Into the Divorce
Even outside those states, you can be pulled into a divorce as a witness or as the subject of discovery requests. If the married partner spent shared marital money on your relationship — trips, gifts, an apartment, hotel stays — the wronged spouse may raise a “dissipation of assets” claim in the divorce. The claim runs against the married spouse, not you, but expect subpoenas, depositions, and records requests aimed at documenting what was spent.
Military Rules Are Different
If you serve in the armed forces, the analysis changes in an important way. Under Article 134 of the Uniform Code of Military Justice, extramarital sexual conduct is a punishable offense.4Office of the Law Revision Counsel. 10 USC 934 Art 134 General Article The maximum punishment includes a dishonorable discharge, forfeiture of all pay and allowances, and up to one year of confinement.
The key point for unmarried service members: your own marital status does not matter. If the person you slept with is married to someone else, you can be charged. The government must prove the sexual intercourse occurred, that at least one participant was married to someone else, and that the conduct was harmful to good order and discipline or brought discredit upon the armed forces.
That last element is where commanders exercise discretion. They weigh the ranks and positions involved, whether government time or resources were misused, the effect on unit morale, whether the service member was ordered to stop and continued anyway, and how public the relationship was. A quiet relationship between people in different units draws less scrutiny than one involving a supervisor and a subordinate’s spouse. The discretion cuts both ways, and service members have faced charges for conduct no civilian court would touch.
When Neither of You Is Married
If both of you are single, cheating carries almost no direct legal consequences. There is no adultery to charge, no fault-based divorce filing available, and no third-party claim for a wronged outsider to bring. Family courts have no jurisdiction over the breakup of an unmarried couple.
The one place law does step in is around money and property. If you and a partner signed a cohabitation agreement or made other financial commitments to each other, a breakup can produce enforceable contract claims. The California case Marvin v. Marvin (1979) held that unmarried partners can sometimes sue each other for a share of property accumulated during the relationship, even without a written agreement, if there was an implied understanding about how assets would be shared. Courts since then have been cautious about how far to extend that reasoning, and the strength of these claims varies by state.
Nothing in that framework is triggered by cheating itself. The legal claim, if one exists, comes from broken financial promises. Infidelity between two unmarried people is not a legal wrong.
What Changes If Children Are Involved
A parent’s romantic life, married or not, rarely shifts custody on its own. Courts decide custody by the best interests of the child, and dating someone new — or being the “other person” in someone else’s affair — does not clear that bar without more. There has to be concrete evidence of harm to the child: unsafe situations, instability, neglect caused by the parent prioritizing the relationship, or something similarly tangible.
Some divorce decrees include “morality clauses” restricting overnight romantic guests when children are present. These are enforceable in some jurisdictions and have been struck down as unconstitutionally vague or as violations of the right to freedom of association in others. Whether one holds up depends on the wording and the state.
Moving a new partner into a home where your children live is the scenario most likely to prompt the other parent to file a modification petition. Judges assess these case by case based on how the change affects the child, not on moral judgments about the parent.
A Word on Trying to Prove It
People who suspect a partner is cheating sometimes log into their email, read their texts, or install monitoring software. Doing so can create serious criminal exposure regardless of marital status. The Federal Wiretap Act makes it illegal to intercept electronic communications, including forwarding a partner’s emails to your own account without their knowledge.5Office of the Law Revision Counsel. 18 USC 2511 Interception and Disclosure of Wire Oral or Electronic Communications Prohibited The Stored Communications Act prohibits accessing stored messages without authorization, carrying up to five years in prison for a first offense committed in connection with any other wrongful act.6Office of the Law Revision Counsel. 18 USC 2701 Unlawful Access to Stored Communications The Computer Fraud and Abuse Act adds another layer, criminalizing unauthorized access to a computer.7Office of the Law Revision Counsel. 18 USC 1030 Fraud and Related Activity in Connection With Computers Evidence obtained this way is often inadmissible on top of the criminal risk. If you need evidence of infidelity for a legal proceeding, work with an attorney who knows the boundaries of lawful investigation.
The Short Version
Adultery is a legal term with a specific requirement, and that requirement is marriage. If you’re not married, and neither is the person you’re seeing, the word doesn’t apply to you. If either of you is married — or if a court could treat your relationship as a common-law marriage — the picture changes quickly. And if you serve in the military, the rules that apply to you are stricter than the ones that apply to civilians, and your own single status won’t protect you.