You're going to have to address two different issues:

The Catholic Church?

Or Western Christianity in general?

In general, and also applying to the Catholic Church, simply put nothing like traditional Christianity is any longer the basis for the Western society. The society that was developed as Christendom and united by the Catholic Church has turned its back, if not on Christ, then on religion and on anything like a traditional interpretation of Christianity.

While his work very long predates the modern day focus on sexuality, you might look at the last two chapters of Hilare Belloc's History of the Great Heresies which discussed the roots of the decline of the Catholic Church and the much more striking ultra-liberalization of most of the Protestant churches.