Answer:
From Ashima's thoughts it is learned that the relationship between Moushumi and Gogol was not a completely happy or satisfactory one.
She is reconciled to the idea of their divorce because she knows continuing a marriage under their circumstances will not be the wise decision for both of them.
Explanation:
After Gogol discovers that Moushumi was having an affair and she confessed to everything, they decided to get a divorce.
Ashima feels guilty for being the one to convince Gogol to meet Moushumi in the first place, and since she realizes that their marriage has never been a wholly happy one she is reconciled to the idea of their divorce.
In Ashima's generation Moushumi and Gogol would have felt it a duty to remain married despite everything that happened, and she thinks, "Fortunately they have not considered it their duty to stay married, as the Bengalis of Ashoke and Ashima's generation do." In her view, the pressure to settle for less than "their ideal of happiness" has given way to "American common sense." And so, Ashima is pleased with this outcome, as opposed to an unhappy but dutiful marriage for her son.
