我只是你的一个备胎而已
        
            [wŏ zhĭ shì nĭ de yī gè bèi tāi ér yĭ]
        
        
            This means 'I am just your spare tire,' referring metaphorically to oneself being kept on standby by someone in case they need a backup option or second choice for a romantic relationship, indicating sadness and inferiority.