你住我心不交钱你住我房不交租
[nĭ zhù wŏ xīn bù jiāo qián nĭ zhù wŏ fáng bù jiāo zū]
This username plays on the idea of a close relationship where one person can 'stay' in the other's heart without needing to 'pay' (emotionally), and also physically staying in the house for free, indicating a deep mutual understanding or dependency between two people.