Synthetic polymerization and supramolecular polymerization with sequence control are far from an easy task. Herein, a narcissistic self-sorting supramolecular polymer is prepared with a sequence of (−AA–BB−) n by using cucurbit8­uril (CB8)-based ternary complexes as supramolecular monomers, which are spontaneously formed from heteroditopic AB-type guest and CB8. Supramolecular polymerization and the structural changes at each stage of polymerization have been successfully demonstrated by NMR, UV–vis, and fluorescence spectra. The self-sorting starts from the second step of polymerization after the formation of different ternary complexes as supra-monomers. The dynamic supramolecular interactions and the thermodynamic stability of the host–guest complexes are found to be the crucial factors to drive the sequence control of the supramolecular polymers. Furthermore, the water-soluble supramolecular polymer is red-emissive and can serve as a fluorescent sensor to detect morphine in artificial urine with considerable stability, sensitivity, and accuracy. And it can also distinguish heroin and morphine, two kinds of opioids with similar structures.