paramour
noun
par·amour
| \ ˈper-ə-ˌmu̇r
, ˈpa-rə-\
, ˈpa-rə-\
Definition of paramour
: lover
specifically
: an illicit or secret lover
a married man and his paramour Her account put him in the position of looking like the duped lover believing the cheating married paramour's protestation of love … — Bettina Drew