philander
verb
phi·lan·der
| \ fə-ˈlan-dər
\
\
philandered;
philandering\ fə-ˈlan-d(ə-)riŋ
\
\
Definition of philander
: to have casual or illicit sex with a person or with many people
especially
: to be sexually unfaithful to one's spouse
—usually used of a man … her philandering brother-in-law; and … the schoolteacher he philanders with. — Judith Crist