What are the ways in which Jhumpa Lahiri presents marriage in the novel The Namesake?

There are a few marriages in Lahiri's The Namesake. Two of these marriages influence Gogol, and one is his own union with Moushumi. 

The first marriage that influences Gogol is, of course, that of his own parents, Ashoke and Ashima. Gogol's parents' relationship is the result of an arranged marriage set up by their parents in India. As a result of this tradition as well as other cultural norms. Ashoke and Ashima are not outwardly affectionate to one another. Gogol reflects at one point that he has never heard his parents say they love each other. However, the reader knows that the two love each other, as demonstrated by the anguish Ashima feels when her husband suddenly passes away. 

Some of Gogol's reflection on his parents' marriage comes from the comparison of the marriage of Gerald and Lydia, the parents of his girlfriend Max. Gerald and Lydia are very openly affectionate and share common intellectual interests. They are comfortable with one another and with expressing their love in front of Max and Gogol. As a result, Gogol notices that Max's parents' marriage is seemingly different from that of his own parents. 

Eventually, Gogol marries not Max but Moushumi, a childhood acquaintance whose parents are also Indian. This relationship seems to fulfill both partners' parents' hopes, but the marriage does not last. Moushumi is unfaithful and wants to disavow some of her connection to her Indian heritage (she is more at home in Europe). Part of the trouble could have stemmed from Gogol's profound struggles with identity. On the whole, the marriages in the novel help the reader evaluate Gogol's ongoing battle to define who he is and who he wants to be.