不能怪小三只能怪你守不住
[bù néng guài xiăo sān zhĭ néng guài nĭ shŏu bù zhù]
This username carries a complex tone related to relationship infidelity. It shifts the focus of blame from a third party involved in a romantic affair (‘little third’ often refers to a homewrecker) to the original couple, specifically criticizing one's partner’s lack of loyalty or commitment to keeping the relationship strong.