不是良人怎会情深
[bù shì liáng rén zĕn huì qíng shēn]
If one is not good enough (a 'virtuous mate'), then why feel such deep emotions? It hints at questioning the depth of someone's love and its authenticity, expressing dissatisfaction with a partner's behavior, attitude, or qualities, especially in romantic relationships. There's often regret over loving a less deserving person.