Portia and Nerissa's friendship is similar to and different from the men's friendship (Bassanio and Antonio's).
1. Similarities: One friend is signficantly wealthier than the other in each of the friendships (Portia and Antonio are able to control much of the play's action because of their wealth), but neither of the wealthier individuals "lords" his or her wealth over friends who have less. Nerissa is Portia's servant, yet Portia seeks advice from Nerissa, treats her as her confidant, and sees her as her intellectual equal. Likewise, even though Bassanio owes Antonio a great deal, Antonio does not manipulate Bassanio with that knowledge, chide him, or hold a grudge against him for the danger his loan to Bassanio causes him. Another similarity is that both sets of friends enter into "schemes" of sorts together. Portia takes Nerissa along with her to Venice, and Nerissa even dresses as a man to help carry out Portia's disguise and mirrors Portia's "ring test" for her own husband. Bassanio entangles Antonio in his quest to win Portia's hand in marriage, showing the same type of trust in his friend as Portia has in hers.
2. Differences: Portia and Nerissa marry at the same time, while Antonio remains a bachelor. Portia and Nerissa seem to use their friendship to exert feminine dominance over males, because Shakespeare gives his audience the impression that the women are more savvy than the men. In contrast, Bassanio and Antony use their friendship only to help each other. Antony is willing to lose his life for Bassanio, and Bassanio is deeply grieved by Antonio's situation and offers up his own life. Their friendship seems deeper and not based upon manipulating others.
3. No, marriage does not really affect Portia and Nerissa's friendship because they marry friends; so physical distance between the two women is unlikely. One could argue that marriage affects Bassanio and Antonio's relationship because Antonio is left alone at the end of the play in contrast to the three married couples.