In the Philippines, the sanctity of marriage is protected by both the Family Code and the Revised Penal Code. While marriage is considered an inviolable social institution, the law provides specific legal avenues for an aggrieved spouse when the marital vow of fidelity is broken. Marital infidelity is not merely a civil wrong but remains a criminal offense, categorized into two distinct crimes: Adultery and Concubinage.

I. The Criminal Aspect: Revised Penal Code

The Philippine legal system distinguishes between infidelity committed by a wife and that committed by a husband. This distinction is rooted in the gender-specific definitions found in the Revised Penal Code (RPC).

1. Adultery (Article 333)

Adultery is committed by a 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.

Evidence: Each individual act of sexual intercourse constitutes one crime of adultery.
Penalty: Prision correccional in its medium and maximum periods.
Key Requirement: The husband must file the complaint against both the guilty wife and the paramour, if the latter is alive.

2. Concubinage (Article 334)

Concubinage is committed by a married man under three specific circumstances. It is generally considered harder to prove than adultery because sexual intercourse alone is insufficient. The husband is liable if he:

Keeps a mistress in the conjugal dwelling;
Has sexual intercourse under scandalous circumstances; or
Cohabits with her in any other place.
Penalty: The husband faces prision correccional in its minimum and medium periods. The concubine is punished with destierro (banishment from a specific radius).
Key Requirement: Like adultery, the wife must sue both her husband and the concubine.

3. Common Provisions

Pardon: The offended party cannot institute criminal prosecution if they have consented to the offense or pardoned the offenders (expressly or impliedly).
Private Crime: These are "private crimes," meaning they can only be prosecuted upon a complaint filed by the offended spouse.

II. Civil Remedies: The Family Code

Beyond criminal prosecution, the aggrieved spouse has several civil remedies aimed at altering the legal status of the marriage or protecting property rights.

1. Legal Separation (Article 55)

Legal separation allows the spouses to live separately and dissolve their absolute community or conjugal partnership, but it does not dissolve the marriage bond. The parties cannot remarry.

Grounds: Sexual infidelity or perversion is a specific ground for legal separation.
Effect on Property: The guilty spouse forfeits their share of the net profits of the conjugal properties.
Cooling-off Period: The law mandates a six-month "cooling-off period" after filing the petition before the trial can begin, to encourage reconciliation.

2. Declaration of Nullity (Article 36)

While infidelity itself is not a ground for annulment, it is frequently used as an evidentiary "manifestation" of Psychological Incapacity.

Theory: A spouse who is chronically unfaithful may be argued to be psychologically incapacitated to comply with the essential marital obligation of mutual love, respect, and fidelity.
Requirement: The incapacity must be grave, have existed at the time of the celebration of the marriage (juridical antecedence), and be incurable.

III. Protection Orders (R.A. 9262)

The Anti-Violence Against Women and Their Children Act of 2004 (VAWC) provides a powerful shield for wives. Infidelity can be classified as a form of Psychological Violence.

Psychological Violence: Causing mental or emotional anguish, including public ridicule or humiliation through marital infidelity, is punishable under this law.
Protection Orders: A wife can seek a Temporary Protection Order (TPO) or Permanent Protection Order (PPO) to remove the husband from the residence or prevent further harassment.
Criminal Liability: Violation of R.A. 9262 carries heavier penalties than the RPC crimes and does not require the same strict "scandalous circumstances" as concubinage.

IV. Damages Under the Civil Code

An aggrieved spouse may also file a civil action for damages against the third party (the paramour or mistress) based on the Human Relations provisions of the Civil Code.

Article 26: "Every person shall respect the dignity, personality, privacy and peace of mind of his neighbors and other persons."
Article 2219: Allows for moral damages in cases of adultery or concubinage. This is a way to seek financial compensation for the emotional distress and social humiliation caused by the affair.

V. Summary Table of Remedies

Remedy	Legal Basis	Result
Criminal Action	RPC Art. 333 / 334	Imprisonment or Destierro for both offenders.
Legal Separation	Family Code Art. 55	Right to live apart; property forfeiture; marriage stays intact.
Nullity of Marriage	Family Code Art. 36	Marriage declared void (if infidelity proves psychological incapacity).
VAWC Case	R.A. 9262	Protection orders; imprisonment for psychological violence.
Civil Damages	Civil Code Art. 26/2219	Monetary compensation for moral and emotional suffering.