unfaithfulness
US /ʌnˈfeɪθ.fəl.nəs/
UK /ʌnˈfeɪθ.fəl.nəs/
1.
infidélité
the fact of having a sexual relationship or experience with a person who is not your husband, wife, or usual sexual partner:
:
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His sister accused their father of adultery and unfaithfulness.