In the Philippines, the sanctity of marriage is protected by the Constitution and the Family Code. While the country does not currently have a general divorce law, the legal system provides for Legal Separation, which allows spouses to live apart and partition their properties without severing the marital bond. Among the most common grounds cited for this remedy is sexual infidelity.

To understand the legal landscape, one must distinguish between the civil ground for legal separation and the specific criminal definitions of adultery and concubinage under the Revised Penal Code.

The Civil Ground: Sexual Infidelity

Under Article 55(8) of the Family Code of the Philippines, a petition for legal separation may be filed on the ground of "sexual infidelity or perversion." Unlike criminal cases, a petition for legal separation is a civil action. This means the burden of proof is a preponderance of evidence—the evidence must be more convincing than that offered in opposition. A criminal conviction for adultery or concubinage is not required to succeed in a civil petition for legal separation.

The Criminal Definitions: Adultery vs. Concubinage

While the Family Code uses the broad term "sexual infidelity," the Revised Penal Code (RPC) distinguishes between the acts of a wife and a husband. This distinction remains a point of significant legal and social debate due to the differing standards of proof required for each.

1. 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.

Requirement: A single act of sexual intercourse is sufficient to constitute adultery.
Participants: Both the wife and her paramour are criminally liable.

2. Concubinage (Article 334, RPC)

Concubinage is committed by a married man under specific, more stringent conditions. To be liable, the husband must perform any of the following:

Keep a mistress in the conjugal dwelling;
Have sexual intercourse with a woman who is not his wife under scandalous circumstances; or
Cohabit with a mistress in any other place.
Distinction: Unlike adultery, a single act of infidelity by a husband outside the conjugal home or without "scandalous circumstances" does not technically meet the criminal definition of concubinage.

Defenses and Bars to Legal Separation

Even if sexual infidelity is proven, the court may deny the petition for legal separation under Article 56 of the Family Code if any of the following are present:

Condonation: Where the innocent spouse has unconditionally forgiven the offense (e.g., continued cohabitation after knowledge of the infidelity).
Consent/Connivance: Where the innocent spouse agreed to or facilitated the commission of the infidelity.
Recrimination: Where both spouses are guilty of a ground for legal separation (e.g., both have committed acts of infidelity).
Collusion: Where the parties have agreed to "manufacture" the ground to obtain a decree.
Prescription: The action must be filed within five years from the time of the occurrence of the cause.

Procedural Requirements

The law imposes a strict "cooling-off period" for legal separation cases. Under Article 58, no trial shall be held on the merits until six months have elapsed since the filing of the petition. This period is intended to give the parties a final opportunity for reconciliation.

During the pendency of the case, the court may issue provisional orders regarding:

Support for the spouses and children.
Custody of minor children.
Administration of common property.

Effects of a Decree of Legal Separation

Once the court issues a decree of legal separation, the following consequences ensue under Article 63:

Separation of Bed and Board: The spouses are entitled to live separately, but they cannot remarry.
Dissolution of Property Regime: The absolute community or conjugal partnership is dissolved and liquidated.
Forfeiture of Profits: The guilty spouse forfeits his or her share of the net profits of the conjugal property in favor of the common children (or the innocent spouse if there are no children).
Custody and Support: Custody of minor children is generally awarded to the innocent spouse.
Disqualification from Succession: The guilty spouse is disqualified from inheriting from the innocent spouse by intestate succession. Moreover, provisions in a will in favor of the guilty spouse are revoked by operation of law.

Summary Comparison

Feature	Adultery (Wife)	Concubinage (Husband)
Legal Basis	Article 333, RPC	Article 334, RPC
Standard of Proof	Single act of intercourse	Scandalous circumstances, cohabitation, or keeping in the home
Civil Remedy	Ground for Legal Separation	Ground for Legal Separation
Marital Status	Marriage remains valid	Marriage remains valid

While the criminal statutes for adultery and concubinage are often criticized for their disparity, they serve as the foundational definitions for "sexual infidelity" in civil proceedings. For an innocent spouse in the Philippines, legal separation remains the primary vehicle for seeking judicial relief and property protection in the face of marital unfaithfulness.