vice
utroskab
infidelity
https://en.wikipedia.org/wiki/Infidelity
https://homosaurus.org/v3/homoit0001647
https://www.wikidata.org/wiki/Q2914621
A violation of a partner's assumed or stated contract regarding emotional and/or sexual exclusivity. Other scholars define infidelity as a violation according to the subjective feeling that one's partner has violated a set of rules or relationship norms; this violation results in feelings of jealousy, sexual jealousy, and rivalry.
cheating
How to Have a Non-Monogomous Relationship