你不是良人怎知我情深
[nĭ bù shì liáng rén zĕn zhī wŏ qíng shēn]
The phrase implies deep affection and regret, where one is addressing someone saying 'how can you truly understand my deep love since you are not the virtuous person for me'. It conveys that only a person who understands the user’s emotions could realize how deep their feelings are, yet they acknowledge that this person might not be suitable for them.