(Philippine legal context; general information only, not legal advice.)

1) The key point most people miss

In the Philippines, you generally cannot file an adultery or concubinage case “against the mistress alone.” These are “private crimes” under the Revised Penal Code, meaning:

Only the offended spouse (the legal wife or legal husband who was cheated on) can initiate the criminal case; and
The complaint must include both guilty parties (your spouse and the third party), if both are alive.

So the “mistress” is typically a co-accused, not the only accused.

2) What crime applies: Adultery vs. Concubinage

The Philippines treats marital infidelity differently depending on whether the offending spouse is the wife or the husband, based on the Revised Penal Code.

A. Adultery (committed by a wife)

Who commits it: A married woman who has sexual intercourse with a man not her husband, and the man who does it knowing she is married.

Bottom line: If the cheating spouse is the wife, the usual criminal case is adultery, and the “other man” is charged with her (if he knew she was married).

B. Concubinage (committed by a husband)

Who commits it: A married man who commits any of the following:

Keeps a mistress in the conjugal dwelling (the family home), or
Cohabits with a mistress in another place (living together as if spouses), or
Has sexual intercourse under scandalous circumstances.

Bottom line: If the cheating spouse is the husband, the usual criminal case is concubinage, and the mistress may also be charged depending on the act alleged.

3) Who can file (standing) and when

Who can file

Only the offended spouse can file the complaint:

For adultery: the husband files.
For concubinage: the wife files.

Generally, no one else can substitute (not parents, siblings, children, friends), because these are private crimes.

When you can file

You must be the offended spouse at the time of filing, and the marriage must be legally existing (no valid decree nullifying the marriage at that time).

4) Legal requirements that can block the case

Even if cheating occurred, prosecution may be barred or undermined by factors commonly raised in these cases:

A. Consent

If the offended spouse consented to the affair (expressly or through clear conduct), prosecution can be barred.

B. Pardon / condonation

If the offended spouse forgave the offenders before filing, that can stop prosecution. Courts examine facts closely—especially whether the forgiveness was clear and voluntary, and whether it effectively covered both offenders.

C. You must include both offenders

A criminal complaint for adultery/concubinage generally cannot proceed if the offended spouse only names one party while the other guilty party is alive and known.

D. Prescription (time limits)

Crimes have prescriptive periods (deadlines), and marital infidelity cases often turn on when the offended spouse discovered the offense and when the complaint was filed. Because this is highly fact-specific and can make-or-break the case, it’s worth getting a lawyer to compute and assess it based on your timeline and evidence.

5) Elements you must prove (what the prosecution needs)

A. Adultery: what must be proven

To convict, the prosecution must establish:

The woman is married;
She had sexual intercourse with a man not her husband; and
The man knew she was married.

Hard reality: The hardest part is proving sexual intercourse, not just intimacy, romance, or spending time together.

B. Concubinage: what must be proven

To convict a husband of concubinage, you generally must prove at least one of the specific modes:

Keeping a mistress in the conjugal dwelling, or
Cohabitation with the mistress elsewhere, or
Sexual intercourse under scandalous circumstances (open, notorious, and offensive to public morals—more than just discreet cheating).

Hard reality: Many affairs do not meet the stricter concubinage definitions, especially if the relationship is discreet and there is no cohabitation or “scandalous circumstances.”

6) Evidence: what helps, what’s risky, what usually isn’t enough

Evidence that can help (lawfully obtained)

Hotel/booking records, receipts, travel records showing opportunity and pairing
Photos/videos taken in public places (no illegal intrusion)
Witness testimony (neighbors, building staff, credible witnesses to cohabitation, etc.)
Messages/communications that show admissions (if obtained without hacking or illegal interception)
Proof of living arrangements (leases, utilities, deliveries, household photos, barangay records, etc.) relevant to cohabitation
Social media posts showing public presentation as a couple (helpful for “scandalous circumstances” arguments, though not automatic)

Evidence that often isn’t enough by itself

Rumors, anonymous tips, “everyone knows”
Flirty messages without more (they suggest a relationship, not necessarily intercourse)
A single photo together
Mere suspicion or “gut feel”

Evidence that can backfire (illegal or high risk)

Wiretapping / recording private conversations without legal authority (the Philippines has strict rules on this)
Hacking accounts, using spyware, illegally accessing phones
Illegally entering a private residence or room to obtain evidence
Posting accusations publicly (could trigger exposure to defamation-type complaints depending on how and where it’s done)

A practical approach is to gather evidence you can defend as lawfully obtained and avoid “shortcuts” that create criminal/civil exposure for you.

7) Where and how you file (process overview)

Step 1: Prepare a complaint-affidavit

Typically you prepare:

A Complaint-Affidavit narrating facts in chronological detail
Supporting affidavits of witnesses (if any)
Documentary evidence (printed screenshots with context, certified records if available)
Proof of marriage (marriage certificate) and identities, plus other relevant documents

Step 2: File with the Office of the City/Provincial Prosecutor (preliminary investigation)

Most adultery/concubinage cases begin with preliminary investigation:

You file the complaint with attachments.
The respondents file counter-affidavits.
The prosecutor determines whether there is probable cause.

Step 3: If probable cause is found, the case is filed in court

If the prosecutor approves, an Information is filed in the proper trial court, and the case proceeds like a criminal case (arraignment, pre-trial, trial).

Venue (where to file)

Usually, venue relates to where the acts occurred—for example where intercourse happened (for adultery) or where cohabitation/keeping in the dwelling occurred (for concubinage). Venue disputes are common in these cases.

8) Penalties (general overview)

Penalties vary by offense and by the proven mode of conduct.

Adultery: The wife and the paramour can face imprisonment penalties set by the Revised Penal Code.
Concubinage: The husband faces imprisonment penalties; the mistress may face a penalty that can include restrictions like banishment-type penalties (e.g., being ordered to stay away from certain places), depending on the exact conviction.

Because penalties involve specific ranges and can change in effect depending on sentencing rules and jurisprudence, lawyers typically explain realistic exposure after reviewing the facts and evidence.

9) What you can do besides (or alongside) a criminal case

Many people pursue non-criminal remedies because criminal proof is demanding and the process is slow.

A. Legal separation

Marital infidelity can be a ground for legal separation, which may include property and custody consequences. (It does not allow remarriage.)

B. Nullity/annulment routes (case-dependent)

Infidelity alone is not “annulment,” but it may relate to broader marital issues depending on the legal theory being used (this is highly fact-specific).

C. VAWC (R.A. 9262) if you are a woman harmed by a partner/husband

If you are a woman and the affair caused psychological violence (e.g., severe emotional distress, humiliation, economic abuse), R.A. 9262 may apply against the husband/partner in appropriate cases. This is not an “adultery/concubinage substitute,” but it can be a more practical route in certain fact patterns (and can include protection orders).

D. Civil damages

Some offended spouses explore civil actions for damages under general civil law principles (e.g., acts contrary to morals, good customs, public policy; abuse of rights). These cases are nuanced and fact-heavy, and success often depends on proving wrongful conduct and damages, not just the affair itself.

10) Practical strategy: how these cases are typically built

If your goal is to file a strong case, most effective preparations focus on:

Locking in your timeline (when you discovered, what you saw, what you can prove, where it happened)
Identifying the correct charge (adultery vs concubinage) and whether the facts fit the legal definition
Gathering lawful, corroborated evidence (not just screenshots—independent proof matters)
Anticipating defenses (consent, pardon, denial, identity, venue, prescription)
Deciding your end goal: punishment, leverage for settlement, protecting children/assets, separation, safety, peace of mind, etc.

11) Frequently asked questions

“Can I file against the mistress only?”

Typically, no—the criminal complaint generally must include both offenders (your spouse and the third party), if both are alive and known.

“Is proof of chatting enough?”

Usually not for conviction. Courts look for proof that meets the elements—especially sexual intercourse (adultery) or the specific qualifying acts (concubinage).

“If we reconciled, can I still file later?”

Reconciliation and forgiveness can be argued as pardon/condonation, which may bar prosecution depending on the facts. If you’re considering reconciliation, it’s wise to understand how that decision may affect legal options.

“Will the case be quick?”

These cases often move slowly, and outcomes depend heavily on evidence strength and whether the facts fit the statute’s definitions.

12) A careful next step

If you’re considering filing, a good immediate move is to write a detailed factual narrative (dates, places, people, how you learned, what proof exists) and inventory evidence you can legally defend. A lawyer can then tell you:

whether facts fit adultery/concubinage (especially concubinage),
whether any bars like prescription/condonation are likely issues, and
what alternative remedies (legal separation, VAWC, civil actions) are more practical for your goals.