From Longman Dictionary of Contemporary Englishcheat on somebody phrasal verbSEX/HAVE SEX WITHto be unfaithful to your husband, wife, or sexual partner by secretly having sex with someone else The magazine claims that almost half of Britain’s women cheat on their partners. → cheat→ See Verb table
Examples from the Corpus
cheat on • What would you do if your boyfriend cheated on you? 