get off with

English

get off with (third-person singular simple present gets off with, present participle getting off with, simple past and past participle got off with)

(UK, Ireland, Commonwealth, slang) To kiss passionately, fondle, or have sex with.
He got off with my sister at the party.
- 1934, Rose Macaulay, Going Abroad, London: Collins, page 222:
  "Hero, obviously, has been getting off with a number of young Basques. I hope her parents won't let it go too far."
- 2007, Dan le Sac vs. Scroobius Pip, "Thou Shalt Always Kill" on Angles
  Thou shalt not express your shock at the fact that Sharon got off with Brad at the club last night by saying "is it?"
Used other than figuratively or idiomatically: see get off,‎ with.
- 1983, James L. Limbacher, Sexuality in World Cinema: L-Z, page 1448:
  [She] masturbates herself for almost two hours and ends up getting off with a bicycle wheel.
- 2018, Quinn Anderson, Cam Boy, page 157:
  Josh […] learned that clients wanted one thing: to watch him get off. Sometimes they got off with him, ordering him to watch them masturbate, or they wanted him to use toys on himself.

The degree of intimacy varies with culture and context, but usually involves a minimum of kissing. In some cases, it is specifically limited to kissing and heavy petting, and excludes sexual intercourse.
The verb is more likely to be used to describe a casual encounter with a stranger or acquaintance than sexual activity in a long-term relationship. Several dictionaries (Cambridge, Collins, Merriam-Webster) define the word euphemistically as "to begin a sexual relationship with someone", but (similar to hook up) the term is often used of situations where no relationship is intended.
In the US, to get off with someone (in an amorous context) is to masturbate or reach orgasm with them.
(In all varieties of English, the words can have various literal meanings, as in she got on the bus with two bottles and got off with only one.)