Miranda is basically Jhumpa Lahiri's version of Carrie from Sex and the City. She's young, naïve, beautiful, and a die-hard romantic who falls in love with the wrong (read: married) guy.
She's also a transplanted, white, mid-Westerner who, you get the sense, has never been with anyone outside of her own culture. In fact, she's never even been with a guy who's taken her out to eat at a fancy restaurant or to the museum (these are things that make her lover Dev so awesome to her).
All of these reasons are why she's super-curious about Dev's culture. She even goes to an Indian grocery store and tries to learn Sanskrit. Now, that's devotion.
Or maybe it's self-delusion. Miranda's in her own fantasy world. That's why she's able to go on with the affair while her co-worker Laxmi talks trash about her cousin's cheating husband. Miranda even asks Dev about his wife and shops for sexy, mistress-y clothes. Maybe it's because Miranda doesn't really know who Dev's wife is. As the narrator points out, "Somehow without the wife there, it didn't seem so wrong" (S 34).
Eventually Miranda feels something like guilt when she meets a little boy who reminds her what affairs can do to someone's life. She decides to let the relationship with Dev go, but it takes a while for her to get to that point. Again—kind of like Carrie and the two TV seasons it takes for her to stop dating Mr. Big (even though she gets back with him at the end of the series—but we don't think Miranda will do that).