对不起我没小三那么伟大
[duì bù qĭ wŏ méi xiăo sān nèi me wĕi dà]
This translates to an ironic or self-mocking expression: 'I am not as great as the other woman (third party in a relationship)' - conveying guilt or dissatisfaction about one's inability to match someone else's capacity to love or be loved.