久伴生情久留生恨
[jiŭ bàn shēng qíng jiŭ liú shēng hèn]
'Staying Together Too Long Brings Affection But Too Long Apart Breeds Resentment.' This implies complex feelings: long-term companionship may lead to genuine affection but if separation drags on for too long, feelings might turn sour leading into bitterness over time.