fremdgehen

Etymology
From, thus “to go strange”, that is “to go with an outsider”.

Verb

 * 1)  to cheat; to be unfaithful have sexual or romantic relations with another than one's stable partner, typically in secret
 * 2)  to be unfaithful; to prefer someone or something else
 * 1)  to be unfaithful; to prefer someone or something else

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