In Philippine family law, adultery (or an extramarital affair) is not a direct ground for annulment or for a declaration of nullity of marriage. It is, however, a recognized ground for legal separation—and it can also trigger criminal liability (adultery or concubinage) and other civil consequences. The confusion often comes from how Filipinos commonly use the word “annulment” to mean “ending a marriage,” even though Philippine law treats annulment, nullity, and legal separation as different remedies with different effects.

This article explains how adultery fits (and does not fit) into these remedies in the Philippine context.

1) Quick guide: three different court remedies

A. Declaration of nullity (void marriage)

This applies when the marriage is void from the start (as if it never legally existed). Common grounds include: lack of essential/formal requisites, bigamous marriages, incestuous marriages, psychological incapacity (Family Code, Art. 36), and others depending on the circumstance.

Effect: parties may generally remarry only after the final judgment and compliance with related requirements (e.g., recording), because the marriage is treated as void—but the court process is still required for civil status correction.

B. Annulment (voidable marriage)

This applies when the marriage is valid at the beginning but can be annulled due to specific defects existing at the time of marriage (Family Code, Art. 45), such as:

lack of parental consent (for certain ages),
unsound mind,
fraud of a kind defined by law,
force/intimidation/undue influence,
impotence,
serious and incurable sexually transmissible disease.

Effect: once annulled by final judgment, parties may generally remarry, subject to legal requirements.

C. Legal separation (valid marriage remains, but spouses live separately)

Legal separation is a remedy where the marriage remains valid and existing, but spouses are legally allowed to live separately and have their property relations adjusted.

Effect: no right to remarry. The marriage bond is not severed.

2) The short answer: adultery is not a ground for annulment; it is a ground for legal separation

Annulment (Art. 45) does not list adultery

The grounds for annulment are exclusive—meaning if the reason is not in the list, it is not a ground for annulment. Adultery is not in that list.

Legal separation (Art. 55) includes “sexual infidelity”

Under the Family Code, one of the grounds for legal separation is “sexual infidelity” (often understood broadly as marital unfaithfulness). This is the civil-law concept used for legal separation, and it is wider than the crime of “adultery” under the Revised Penal Code.

So, in civil family law: extramarital affairs → legal separation (possible), not annulment (not by itself).

3) Why adultery doesn’t “invalidate” a marriage

Annulment and nullity focus on defects that exist at the time of marriage (or legal causes that make a marriage void from the start). Adultery usually occurs after the marriage is celebrated, and as serious as it is, it generally does not show that the marriage was void or voidable at inception.

In other words:

Annulment/nullity asks: Was there something legally wrong with the marriage at the start?
Legal separation asks: Did a serious marital offense happen during the marriage that justifies separation?

Adultery typically falls into the second category.

4) The important nuance: adultery may be “evidence,” but it still isn’t the “ground” for annulment/nullity

This is where people get misled. An affair can appear in cases that end in “annulment” (as people commonly say), but legally:

A. Infidelity is sometimes alleged in psychological incapacity cases (Art. 36)

A spouse’s chronic, extreme, or pathological unfaithfulness may be argued as a symptom of psychological incapacity to comply with essential marital obligations (like fidelity, respect, and mutual support). However:

The legal ground is psychological incapacity, not adultery.
Courts typically look for proof that the incapacity is rooted in the spouse’s psychological makeup, is serious, and is present at the time of marriage (even if it becomes evident later).
Mere “cheating,” even repeated cheating, is not automatically psychological incapacity. The law does not treat moral failure alone as equivalent to legal incapacity.

Practical takeaway: An affair can be part of the story, but you still must prove the legal standard for psychological incapacity; otherwise the case fails.

B. Infidelity after marriage is not fraud for annulment

“Fraud” as a ground for annulment is limited to specific types recognized by law (Family Code, Arts. 45(3) and 46). Cheating that happens after the wedding is generally not the kind of fraud contemplated because it is not a deception that induced consent at the time of marriage.

C. When can “fraud” relate to sexual matters?

Fraud for annulment is not a catch-all. The Family Code recognizes fraud in specific forms, such as (among others):

concealment of pregnancy by another man at the time of marriage,
concealment of a sexually transmissible disease, serious and incurable,
concealment of conviction of a crime involving moral turpitude,
and other legally recognized fraudulent acts under the Code.

These are not the same as adultery. But they show how sexual or relational deception might become relevant—again, only if it fits the legal definition of fraud and existed at the time of marriage.

5) Legal separation based on sexual infidelity: what it does and does not do

What legal separation can give you

If granted, legal separation generally results in:

the right to live separately (“separation from bed and board”),
dissolution of the property regime (e.g., conjugal partnership/absolute community) and division/liquidation per law,
custody and support orders,
potential forfeiture of the offending spouse’s share in certain property benefits in favor of common children (subject to the Code and case specifics),
rules on inheritance rights may be affected in specific ways.

What legal separation cannot give you

You cannot remarry. The marriage bond remains.
The civil status remains “married,” though legally separated.

Procedural and legal guardrails (why it’s not as simple as “prove cheating”)

Legal separation has built-in restrictions intended to protect marriage as a social institution. Common features include:

a statutory “cooling-off” period before trial in many cases (with exceptions where safety is at issue),
the State’s participation (through the prosecutor) to prevent collusion,
defenses like consent, connivance, or forgiveness (condonation) in proper cases,
prescription: actions must generally be filed within a time limit from the occurrence of the cause.

This means even if an affair happened, the court still examines whether the action was filed on time, whether there was forgiveness, and whether the evidence meets the required standard.

6) “Adultery” vs “sexual infidelity” vs “concubinage”: civil and criminal concepts differ

A. Criminal law: adultery and concubinage (Revised Penal Code)

In criminal law:

Adultery traditionally refers to a married woman having sexual intercourse with a man not her husband, and the man knowing she is married.
Concubinage traditionally refers to certain acts by a married man (e.g., keeping a mistress in the conjugal dwelling, having sexual intercourse under scandalous circumstances, or cohabiting with the mistress), with penalties and elements different from adultery.

Key criminal-law features often include:

Only the offended spouse can file the complaint (it is typically not prosecuted by the State without the spouse’s complaint).
The complaint commonly must include both the offending spouse and the paramour/partner, if known and liable.
Consent or pardon can bar prosecution in certain circumstances.

Criminal cases are about punishment; they do not, by themselves, dissolve or annul a marriage.

B. Civil family law: “sexual infidelity” for legal separation

“Sexual infidelity” as a ground for legal separation is broader and focuses on marital breach, not technical criminal elements. Some conduct may justify legal separation even if it is difficult to prosecute criminally (and vice versa).

7) Alternative remedies people confuse with “annulment” when there is adultery

A. Declaration of nullity based on psychological incapacity (Art. 36)

As explained, infidelity can be relevant as evidence, but the case succeeds only if the stringent legal standard is met.

B. Violence Against Women and Children (VAWC) implications (RA 9262)

In some situations, an extramarital affair (especially when accompanied by humiliation, harassment, economic abuse, or coercion) may be part of a pattern that supports claims of psychological or economic abuse under VAWC. This is a different legal track from annulment/legal separation and depends on specific facts.

C. Support, custody, property protection, and protection orders

Even without annulment or legal separation, spouses may seek:

child support orders,
custody arrangements,
protection orders (where applicable),
property reliefs (depending on the situation and available causes of action).

8) Practical comparisons: choosing the correct legal concept for the problem

If the goal is: “I want to end the marriage so I can remarry”

Legal separation will not achieve this.
The usual paths are declaration of nullity (if void) or annulment (if voidable), but adultery alone is not enough.

If the goal is: “My spouse cheated, and I want a court-recognized separation with property and custody orders”

Legal separation is the remedy where “sexual infidelity” is directly relevant.

If the goal is: “I want my spouse (and/or the third party) punished”

That is in the realm of criminal law (adultery/concubinage), subject to strict requirements.

If the goal is: “I need immediate safety or protection”

The correct remedy may involve protective orders and other urgent relief, depending on facts.

9) Bottom line in Philippine law

Adultery (or an affair) is not a ground for annulment under the Family Code’s exclusive list of annulment grounds.
Sexual infidelity is a ground for legal separation, which does not allow remarriage because the marriage bond remains.
An affair may appear in cases that result in a marriage being declared void (especially under psychological incapacity), but the legal ground is not adultery—it is the proven defect (e.g., psychological incapacity) meeting the legal standard.
Adultery/concubinage may lead to criminal liability, but criminal prosecution is separate from changing civil marital status.