A. The plaintiff and C are legally married couple who completed the marriage report on December 16, 1980, and have children under the sleep.

B. The Defendant knew that C had a spouse by marriage, and had established a relationship with C from around 2000 to around 2017.

[Ground of recognition] Facts without dispute, Gap evidence 1 to 3, Eul evidence 2 and 3, the purport of the whole pleadings

2. Determination

(a) Husband and wife shall live together, and have the obligation to support and cooperate with each other;

(Article 826 of the Civil Act). Husband and wife, as a community in which mental, physical, or economic combination is achieved, shall have the duty to cooperate and protect each other in a comprehensive manner so that marriage as a marital community is maintained, and shall have the right to such a duty.

As such, as the content of the marital or marital life maintenance obligation, the married couple bears the sexual duty that should not commit any unlawful act.

The "Cheating" here is a broad concept, including the adultery, which does not reach the gap, but includes all unlawful acts that do not fulfill the duty of mutual assistance of the couple. If one of the married couple commits an unlawful act, the other spouse is liable to compensate for the mental suffering suffered by the spouse.

On the other hand, a third party shall not interfere with a married couple’s community life, which is the essence of the marriage, such as interfering with a couple’s community life by interfering with another person’s community life.

In principle, a third party's act of infringing on or interfering with a marital life falling under the essence of marriage by committing an unlawful act with either side of the married couple and causing mental pain to the spouse by infringing on the rights of the spouse as the spouse.

(See Supreme Court Decision 2013Meu2441 Decided May 29, 2015, and Supreme Court Decision 88Meu7 Decided May 24, 198, etc.). (B)

The above facts are examined in light of the legal principles.