Marriage in the Philippines is a permanent institution under the Family Code, with spouses obligated to mutual love, respect, fidelity, and support. When one spouse engages in sexual infidelity, the aggrieved spouse has recourse through criminal prosecution for adultery or concubinage under the Revised Penal Code (RPC) and civil remedies, primarily legal separation under the Family Code. Infidelity may also support a petition for declaration of nullity of marriage if it manifests psychological incapacity. These remedies address the breach while accounting for the absence of absolute divorce in Philippine law for non-Muslim citizens.

Criminal Liability: Adultery and Concubinage

The RPC penalizes marital infidelity as crimes against chastity, with distinctions based on the offending spouse's gender.

Adultery (Article 333, RPC) occurs when a married woman has sexual intercourse with a man who is not her husband, and the man knows or has reason to know that she is married. The marriage need not be valid at the time of prosecution if it existed during the act. Both the wife and her paramour are principals and face liability.

Concubinage (Article 334, RPC) applies to a married man who:

Keeps a mistress in the conjugal dwelling;
Has sexual intercourse with a woman who is not his wife under scandalous circumstances; or
Cohabits with her in any other place.

The husband is the principal offender, and the mistress (concubine) is liable as an accomplice.

Penalties:

Adultery: Prisión correccional in its medium and maximum periods (2 years, 4 months and 1 day to 6 years) for both the wife and paramour.
Concubinage: Prisión correccional in its minimum and medium periods (6 months and 1 day to 4 years and 2 months) for the husband; the concubine faces destierro (banishment).

These are private crimes. Only the offended spouse may initiate prosecution by filing a complaint that includes both guilty parties (if alive). Third parties, such as family members, lack standing. The offended spouse must still be legally married to the accused at the time of filing. Consent to the act, express or implied pardon, or condonation (e.g., resuming marital relations after knowledge of the infidelity) bars prosecution.

Prescriptive period follows general rules for correctional penalties (typically 10 years), but prompt action is essential to avoid implied condonation or evidentiary challenges.

Filing process for criminal cases:

Gather admissible evidence (e.g., photographs, messages, witness testimonies, hotel records, or affidavits proving sexual relations and knowledge of marriage).
Prepare a sworn Complaint-Affidavit detailing the facts, elements of the offense, and supporting evidence.
File the complaint with the Office of the City or Provincial Prosecutor in the place where the offense was committed (territorial jurisdiction).
The prosecutor conducts a preliminary investigation: subpoena the respondents (unfaithful spouse and third party) for counter-affidavits, reply, and possible clarificatory hearings.
If probable cause is found, the prosecutor files an Information in the appropriate court (usually Metropolitan or Municipal Trial Court given the penalties).
Proceedings continue with arraignment, pre-trial, trial on the merits, and judgment. The burden of proof is beyond reasonable doubt.

Conviction results in imprisonment, possible civil liability for damages, and serves as strong evidence in related family court cases.

Repeated or scandalous infidelity may also constitute psychological violence under Republic Act No. 9262 (Anti-Violence Against Women and Their Children Act), allowing the wife (or in some interpretations, the aggrieved party) to file a separate criminal case with penalties of 6 years and 1 day to 12 years imprisonment, plus protection orders.

Civil Remedy: Legal Separation

Sexual infidelity or perversion is an explicit ground for legal separation under Article 55(8) of the Family Code. This applies regardless of gender and covers extramarital sexual relations or grossly inappropriate sexual conduct.

Other grounds under Article 55 include repeated physical violence, moral pressure to change religious or political affiliation, attempt to corrupt into prostitution, conviction to more than six years imprisonment, drug addiction or habitual alcoholism, lesbianism or homosexuality, bigamous marriage, attempt on the petitioner's life, or abandonment for more than one year.

Process for legal separation:

The aggrieved spouse (petitioner) files a verified petition in the Regional Trial Court (Family Court) of the place where the petitioner or respondent resides.
Pay docket fees and serve summons on the respondent.
The court observes a mandatory six-month cooling-off period from filing before trial (Article 58, Family Code) to encourage reconciliation.
Parties may undergo mediation or counseling.
If unresolved, trial proceeds with evidence of the ground (preponderance of evidence standard).
The court issues a decree of legal separation if granted.

Effects of the decree (Article 63, Family Code):

Spouses may live separately but remain legally married (no remarriage possible).
The absolute community of property or conjugal partnership is dissolved and liquidated; the offending spouse is disqualified from any share in the net profits.
The offending spouse is disqualified from inheriting from the innocent spouse by intestate succession and may lose testamentary benefits.
Custody of children is awarded based on the best interest of the child; legitimate children remain legitimate.
Support obligations for the spouse and children continue, chargeable against the properties.
The innocent spouse may revoke donations made to the offending spouse during the marriage.
The decree may include provisions on surname use and visitation rights.

Reconciliation is possible by filing a joint manifestation under oath; the court issues a decree reviving the marriage's legal effects.

Declaration of Nullity of Marriage (Psychological Incapacity)

Infidelity alone does not constitute a ground for annulment or nullity. However, under Article 36 of the Family Code, a marriage is void if one or both spouses were psychologically incapacitated at the time of celebration to fulfill essential marital obligations (including fidelity), provided the incapacity is grave, juridically antecedent, and incurable.

Courts evaluate the totality of evidence. Sexual infidelity, when combined with abandonment, failure to support, multiple affairs, or other behaviors indicating a fundamental inability to understand marital duties, may demonstrate psychological incapacity. Expert psychological testimony is helpful but not always mandatory; lay testimonies from family, friends, or the spouse can suffice if they show the root cause predated the marriage.

Process: File a petition in the Regional Trial Court (Family Court). The Solicitor General and a prosecutor represent the State. Proceedings involve evidence, possible psychological evaluation, and a decision subject to appeal. If granted, the marriage is declared void ab initio, allowing remarriage and liquidation of properties as if no marriage occurred.

Annulment under Article 45 (voidable marriages) has limited grounds (e.g., fraud, impotence) that rarely encompass post-marriage infidelity.

Evidence, Proof, and Practical Considerations

Evidence in both criminal and civil cases commonly includes:

Testimonies of witnesses who observed the affair.
Documentary proof: text messages, emails, social media posts, hotel receipts, photographs, videos, or travel records.
Admissions or confessions.
Birth records of children born from the affair (for impugning legitimacy under Article 166, Family Code, within prescribed periods).

Evidence must be obtained legally; illegally seized materials may be excluded. DNA testing may establish paternity of children from the affair, affecting support and inheritance.

Venue and jurisdiction: Criminal complaints go to the prosecutor's office and court where the act occurred. Family cases are filed where the parties reside.

Children: Legitimate children retain status and rights to support and inheritance. The innocent spouse typically receives preference in custody, subject to the child's best interests. The unfaithful spouse remains obligated to support children, including any illegitimate ones from the affair.

Property and support: The property regime is governed by the marriage settlement or default rules (absolute community or conjugal partnership). Legal separation or nullity triggers liquidation, with protections for the innocent spouse and children.

Special considerations:

The law treats husbands and wives differently in criminal penalties, a feature subject to ongoing reform proposals.
For Muslim Filipinos under Presidential Decree 1083, divorce options (e.g., talaq, faskh) may apply alongside or instead of these remedies.
Overseas Filipino workers or cases with foreign elements may involve conflict of laws, recognition of foreign judgments, or consular assistance.
Costs include filing fees, lawyer's fees, and potential psychological evaluations. Indigent litigants may access the Public Attorney's Office.
Emotional toll is significant; many cases involve parallel proceedings (criminal, legal separation, and custody/support).

The Philippine legal framework balances punishment of infidelity with opportunities for reconciliation while protecting the innocent spouse, children, and family assets. Each case turns on specific facts, timing, evidence, and the parties' conduct after discovery of the infidelity.