From Longman Dictionary of Contemporary Englishgo off with something/somebody phrasal verb informal1 RELATIONSHIPto leave your usual sexual partner in order to have a relationship with someone else She’s gone off with her husband’s best friend.2 STEALto take something away from a place without having permission Who’s gone off with my pen? → go→ See Verb table
Examples from the Corpus
go off with • She went off with this bloke from the garage. 