Under Philippine law, marital infidelity is not merely a moral failing but a criminal offense. For Filipinos residing or working abroad (Overseas Filipino Workers or OFWs), seeking legal redress against a spouse and their partner (the mistress or paramour) presents unique jurisdictional and procedural challenges.

1. Defining the Offenses: Adultery vs. Concubinage

The Revised Penal Code (RPC) distinguishes between infidelity committed by a wife and that committed by a husband.

Adultery (Article 333)

Committed by: A married woman who has sexual intercourse with a man not her husband.
The Co-Defendant: The man who has carnal knowledge of her, knowing her to be married, is also liable.
Evidence Required: Proof of a single act of sexual intercourse is sufficient for conviction.

Concubinage (Article 334)

Committed by: A married man under specific circumstances. Unlike adultery, sexual intercourse alone is not enough. The husband must have:

Kept a mistress in the conjugal dwelling; OR
Had sexual intercourse under scandalous circumstances; OR
Cohabited (lived together) with her in any other place.

The Co-Defendant: The concubine is liable if she knows the man to be married. However, her penalty is generally destierro (banishment from a specific radius) rather than imprisonment.

2. Jurisdictional Realities: The "Territoriality Rule"

A fundamental principle of Philippine criminal law is territoriality. Crimes are punishable only if committed within Philippine territory.

Acts Committed Abroad: If the illicit affair and the acts of cohabitation or intercourse occur entirely outside the Philippines (e.g., in Dubai, Singapore, or Italy), Philippine courts generally do not have jurisdiction to try the criminal case of Adultery or Concubinage.
The Exception: If any of the essential elements of the crime (such as a specific act of scandalous intercourse or a period of cohabitation) occurred while the parties were in the Philippines, a case may be filed.

3. Filing from Abroad: Procedural Steps

If the elements of the crime occurred in the Philippines, an aggrieved spouse living abroad can still initiate a criminal complaint.

Step 1: Execution of the Complaint-Affidavit

The offended spouse must prepare a Complaint-Affidavit. Since the complainant is abroad, this document must be:

Signed in the presence of a Philippine Consular Officer at the nearest Embassy or Consulate.
Consularized/Authenticated: This serves the same purpose as notarization in the Philippines.

Step 2: Appointment of an Attorney-in-Fact

While not strictly required for the signing of the criminal complaint (which the victim must do personally), it is highly practical to execute a Special Power of Attorney (SPA). This allows a representative or legal counsel in the Philippines to file the documents with the Office of the City or Provincial Prosecutor and attend preliminary hearings.

Step 3: Preliminary Investigation

The Prosecutor will determine if there is probable cause. If the respondents (the spouse and the mistress/paramour) are also abroad, the Prosecutor will issue subpoenas to their last known Philippine addresses.

4. Evidentiary Requirements

Cases of infidelity are notoriously difficult to prove because "carnal knowledge" usually happens in private. Evidence typically includes:

Testimonial Evidence: Statements from witnesses who saw the parties living together or acting as husband and wife.
Documentary Evidence: Birth certificates of children born out of the illicit relationship (where the husband signs the birth certificate as the father), social media posts, flight records, or hotel receipts.
Photographic/Video Evidence: Must be authenticated to be admissible in court.

5. The Rule of Prosecution: Total Bar

Under Article 344 of the RPC, the offended spouse cannot institute a criminal case if:

They have consented to the offense.
They have pardoned the offenders (expressly or impliedly).
The "All or Nothing" Rule: The complainant must include both the guilty spouse and the mistress/paramour in the complaint. You cannot choose to sue only the mistress and spare the spouse.

6. Civil Alternatives: Psychological Violence

For many OFWs, if the criminal case for Concubinage fails due to the territoriality rule, they may look toward Republic Act No. 9262 (Anti-Violence Against Women and Their Children Act).

The Philippine Supreme Court has ruled that a husband’s marital infidelity, even if committed abroad, can cause psychological violence to the wife in the Philippines. Since the "mental or emotional anguish" (an element of the crime) is felt by the wife while she is in the Philippines, Philippine courts may exercise jurisdiction over a VAWC case even if the physical acts of infidelity happened overseas.

Important Note on Extradition

Adultery and Concubinage are generally not included in extradition treaties. Even if a warrant of arrest is issued in the Philippines, it is unlikely the offenders will be forcibly returned from abroad solely for these charges. However, the warrant remains active, and they may be arrested immediately upon re-entry into the Philippines.