In The Great Gatsby what does myrtle think about her marriage?

No, Tom doesn't want to divorce Daisy and marry Myrtle instead- he finds a 'lower class' mistress to have an affair with, just because he can, and due to his arrogance and Hubris, it makes sense that Tom would do this for his own amusement. Also, the fact that Tom 'accidently' breaks Myrtle's nose when she mentioned Daisy helps us to understand that Tom doesn't actually Myrtle- in fact, it's out of the question.