A curing agent composition contains at least one multifunctional aromatic amine that forms a crystalline solid at 25°C, and at least one halo-substituted diethyltoluenediamine, in an amount effective to inhibit crystallization of the at least one multifunctional aromatic amine. A curable resin composition contains at least one epoxy compound having at least two epoxide groups per molecule of the epoxy compound and the curing agent composition. Methods for inhibiting phase separation of a curing agent composition or curable resin composition that contains at least one multifunctional aromatic amine that forms a crystalline solid at 25°C include a step of adding to the respective composition at least one halo-substituted diethyltoluenediamine in an amount effective to inhibit crystallization of the at least one multifunctional aromatic amine. The compositions and methods are useful in making fiber reinforced resin matrix composite articles.