Can you lose a lawsuit against the affair partner even with clear evidence of the affair?

“We even have photos of them going into a motel together. Could we still lose?” When we hear this question, we first ask back not about the scene in the photo but about what that person knew. A claim for compensation for emotional distress against an affair partner is not a divorce case but a damages case for a tort under Article 750 of the Civil Act. A tort requires intent or negligence on the part of the person who acted.

Your spouse's wrong and the affair partner's wrong are assessed separately

The fact that your spouse had an affair shows your spouse's wrongdoing. To hold the affair partner liable, there must be a separate wrong attributable to that person. The Supreme Court holds that a third party who commits an unchaste act with one spouse and thereby infringes the couple's shared married life in principle commits a tort, and is jointly liable with the spouse as a joint tortfeasor (Supreme Court Decision 2013Meu2441, May 29, 2015). The words to note here are infringement of the couple's shared married life, and acting with knowledge of it. This is also why you can bring a claim against the affair partner alone without divorcing. Even if the marriage continues, the harm of the infringement of shared married life remains.

The three things the court checks

In practice, courts generally look at three things separately. If even one is missing, the outcome is shaken no matter how much other evidence there is.

• Whether the two were in a romantic relationship. Even if sexual intercourse cannot be proven, a relationship that breaches the duty of fidelity amounts to an unchaste act.
• Whether the affair partner knew, or could have known, that your spouse had a family.
• Whether your shared married life was actually continuing at the time.

In consultations, we often see plenty of material on the first question while the second and third are almost empty. A hotel receipt shows the relationship, but it does not go so far as to show that the affair partner knew your spouse was married.

Case law does not go so far as to impose a duty to check whether a romantic partner has a spouse. So a vague claim that the affair partner could have known carries little force; it needs specific circumstances, such as your spouse always wearing a wedding ring or being out of contact every weekend because of family plans.

How to fill the gaps

Knowledge of the marriage is most often revealed in the two people's conversations. Typical examples are talk about the children, remarks about being careful around the spouse, and pressure to get a divorce. If there are no such conversations, gather indirect material period by period, such as a messenger profile with family photos, or the fact that they met at a workplace or group where the marriage was known.

The fact that the marriage was continuing is surprisingly easy to forget. Ordinary records showing that you lived in the same home, shared living expenses, and spent holidays and children's events together block the other side's claim that the marriage had broken down. The affair partner who claims the marriage had already broken down must prove it (Supreme Court Decision 2022Meu13504, 13511, June 27, 2024), but having rebuttal material ready in advance makes the trial proceed much more steadily.

Before writing the complaint, try sorting the material you have into a three-column table. The empty column is where the other side will attack. As you fill in the table, you may find you have more material than you thought, or you may conclude that you should not file the complaint yet. Either way, that judgment needs to be made before filing.