哥非妳不娶姐非你不嫁
[gē fēi năi bù qŭ jiĕ fēi nĭ bù jià]
The meaning here is 'Brother won't marry if it’s not you; Sister won't marry if it’s not you', expressing intense, unwavering love for someone specific that can almost verge on being possessive or an unyielding obsession.