In the Philippines, the sanctity of marriage is protected by the Constitution and reinforced by penal laws. While "infidelity" is the general term for marital unfaithfulness, the Revised Penal Code (RPC) distinguishes between the legal actions available against a husband and a wife. Specifically, a husband may be charged with Concubinage, while a wife may be charged with Adultery.

1. Understanding Concubinage (Article 334, RPC)

Unlike adultery, which is committed by a simple act of sexual intercourse between a married woman and a man not her husband, Concubinage has a higher threshold of proof. A wife can only file a criminal case for concubinage against her husband if he commits any of the following:

Keeping a mistress in the conjugal dwelling: The husband brings his paramour to live in the same house where he and his wife reside.
Sexual intercourse under scandalous circumstances: The husband and his mistress are not living together, but their relationship is so public or flaunted that it causes public outcry or dishonor to the marriage.
Cohabiting with a mistress in any other place: The husband and his mistress live together as "husband and wife" in a separate residence (e.g., an apartment or a "second home").

Penalties:

For the Husband: Prision correccional in its minimum and medium periods (6 months and 1 day to 4 years and 2 months).
For the Mistress: Destierro (banishment). The mistress is prohibited from entering a designated radius (typically 25 to 250 kilometers) from the residence of the couple for a specific period.

2. Understanding Adultery (Article 333, RPC)

Adultery is committed by any married woman who has sexual intercourse with a man not her husband, and by the man who has carnal knowledge of her knowing her to be married.

Proof required: A single act of sexual intercourse is sufficient to constitute adultery.
Penalties: Both the wife and her paramour face prision correccional in its medium and maximum periods (2 years, 4 months, and 1 day to 6 years).

3. Civil Actions: Legal Separation and Annulment

Criminal prosecution is not the only recourse. Victims of infidelity often seek civil remedies to address the status of their marriage and properties.

Legal Separation (Article 55, Family Code)

Infidelity is a ground for legal separation. Under Philippine law, a petition may be filed based on:

Sexual infidelity or perversion.
Moral pressure to change religious or political affiliation.
Attempt of the respondent against the life of the petitioner.

Effect: The spouses are entitled to live separately, and the absolute community or conjugal partnership is dissolved and liquidated. However, the marriage bond remains intact, meaning neither party can remarry.

Declaration of Nullity (Article 36, Family Code)

If the infidelity is a manifestation of a deeper "Psychological Incapacity," the offended spouse may file for a Declaration of Nullity of Marriage. The petitioner must prove that the infidelity is a symptom of a personality structure that renders the spouse incapable of complying with the essential marital obligations. If granted, the marriage is declared void from the beginning (void ab initio), allowing parties to remarry.

4. Violence Against Women and Their Children (R.A. 9262)

The Supreme Court has recognized that marital infidelity can cause severe emotional and psychological distress to the wife. Under Republic Act No. 9262 (VAWC), infidelity may be categorized as Psychological Violence.

A wife may file for a Protection Order (Barangay, Temporary, or Permanent) to prevent the husband from further harassing or communicating with her.
The husband can face significant prison time and mandatory psychological counseling if proven that his infidelity caused "mental or emotional anguish" to the wife.

5. Essential Procedural Rules

Pardon and Consent: A criminal complaint for adultery or concubinage cannot be pursued if the offended party has consented to the offense or pardoned the guilty parties (Article 344, RPC).
Prosecution: These are "private crimes." Only the offended spouse can initiate the criminal complaint.
The "Double standard" Issue: Legal scholars often note the disparity between the requirements for Adultery (one act) vs. Concubinage (cohabitation/scandal). While there have been legislative attempts to unify these under a gender-neutral "Marital Infidelity" law, the RPC definitions currently remain in force.

6. Summary of Legal Remedies

Remedy	Legal Basis	Result
Criminal Case	RPC Art. 333/334	Imprisonment or Destierro for the guilty parties.
VAWC Case	R.A. 9262	Protection orders and penalties for psychological abuse.
Legal Separation	Family Code Art. 55	Separation of bed and board; dissolution of property.
Annulment/Nullity	Family Code Art. 36/45	Complete severance of the marriage bond.