心太窄只能让你一人走心太小只容得下你一人
[xīn tài zhăi zhĭ néng ràng nĭ yī rén zŏu xīn tài xiăo zhĭ róng dé xià nĭ yī rén]
The phrase expresses the deep and exclusive love towards one person, indicating that their heart is only big enough for one person and there is no space for anyone else.