People who are still living as an Orthodox Jew to the outside but on the inside have left Orthodox Judaism, have to deal with living in two worlds: the orthodox home / society / family on the one hand, and the personal beliefs and private actions of this person on the other hand.
There is a widespread misconception (based on Sanhedrin 63) that the only reason why people leave observance is to indulge in their desires. In general, we can say that there are plenty emotional and rational reasons why people leave Orthodox Judaism.
Rational reasons include:
Some emotional reasons could include:
To learn more about some reasons why people leave observant Judaism, the book Off the Derech by Faranak Margolese can be helpful, although many ex-observant people disagree with some of the premises and conclusions in the book. Nevertheless, it is the only book so far that seems to address the issue of why people leave orthodoxy.