A nursery pollinator system comprises a plant and an insect pollinator which uses the reproductive structures of the plant to guard its eggs and serve it as food for the larvae. This kind of systems usually includes a third party, one or more species of parasitoids, that inject their eggs inside the larvae of the pollinating-seed predator to feed on them from the inside out. Here we build a model based on differential equations that replicates this system, first by showing the dual role of the pollinating-seed predator, which behaves both as a mutualist and as antagonist for the plant. We show that the system is more stable with the presence of the parasitoids; the stationary solutions with them significantly favor the plant population size with minor effects for the population of the pollinating-seed predator. By modeling both sexes of the nursery pollinator separately, we also highlight the role that male adults can have to compensate the costs and benefits of the interaction with plants, and thus to contribute to the stability of such mutualisms.