雙宿雙飛 [双－双飞]

Jyutping soeng1 suk1 soeng1 fei1
Pinyin shuāng sù shuāng fēi

Definitions (CC-CEDICT)
  1. lit. to rest and fly together (idiom)
  2. fig. to live in each other's pockets
  3. to be inseparable
Definitions (Wiktionary)
  1. phrase, idiomatic, of a pair of lovers
    to be intimate and inseparable; to live in each other's pockets