I disagree, Paul has actually undergone some changes. He talks a lot more with Leora and shows more signs of affection than when they were together in Russia. The Old Paul would have reacted very badly to Leora's outburst the other day, when they were in bed and Leora felt resentful of something. Instead he was calm enough to be able to bring everything back to normal (and I think Leora also realized that she behaved unfairly badly with Paul that time). On some things it has remained the same, that is true, but we see that there are still changes in attitude, even if they are few. Even for the sex too he is striving to last longer.
And I don't think he does it for money, we know that for Paul (and for Leora) sex has never been of primary importance. In the old apartments, weeks could go by without Paul having sex with Leora. Now, however, at least a couple of times a week they do something quite regularly and it seems that they are fine with it.