extramarital affair

Translations
внебрачная связь
Someone discovered their partner's extramarital affair.
Кто-то обнаружил внебрачную связь своего партнера.
Definitions
A romantic or sexual relationship that occurs between a married person and someone who is not their spouse, typically considered to be a breach of marital fidelity.
Words
extramarital

adjective
внебрачный
affair

noun
связь