Given that there are 100 stories in Boccaccio's Decameron, it is difficult to generalize about how gender roles are portrayed in the work. Many of the stories are retellings of older tales, and so multiple viewpoints are reflected.
A good way to approach the topic would be through Bakhtin's notion of the carnivalesque, of seeing both the time of the plague and retreat to the villa, as a carnival or saturnalia, in which ordinary rules are inverted or dispensed with. Thus we seeing a breaking down of gender roles and categories.
A distinct feature of many of the details, whatever the gender of the narrator, is that while women are realistically portrayed as politically disempowered, and, with the exception of widows, economically disadvantaged, they are sexually powerful, active, and transgressive, and what they cannot achieve via authority they manage via cunning. While the relationships among men have considerable variety, including friendship, jealousy, etc., relationships between men and women (other than familial ones) are purely sexual, with women being portrayed as just as lustful as men. This is true in the tales of both male and female narrators.