Supramolecular polymer systems consist of polymers with bonding groups that can form reversible inter-polymer linkages. In multi-component polymer systems, these reversible bonds play a key role in the self-assembly of these polymers into inhomogeneous phases. Moreover, these materials hold great technological promise as experiments have shown that temperature can be used to control the morphology and hence the material properties of the system. To understand the equilibrium phase behavior of these polymeric materials, we develop a field-theoretic model for a system in which an A and B homopolymer can reversibly bond to form a diblock copolymer. A free energy of bonding governs the strength of this reversible bond. Using self-consistent field theory, we calculate a mean-field phase diagram for a symmetric system in which the A and B homopolymers are the same length and occupy the same volume. For certain values of parameters, we find re-entrant phase behavior in which the system passes through a lamellar, a disordered and then another lamellar phase with decreasing temperature.