You do not "turn gay". Your sexual preference is part of who you are, and what actually determines it is extremely complicated and best answered by people who study the physiology and psychology of humans. In laymans terms, however, you are or are not gay. What people tend to think of as "turning gay" is actually a misconception. We live in a sexually repressed society, where sexuality and sexual exploration are not encouraged and people who engage in consensual sexual exploration are often ostracized and shamed. Because we are not encouraged to explore our sexuality as we go through adolescence, some people find that once they are on their own, experiencing the broader world outside of their parents' influence that they have sexual urges that they did not recognize before. This could have been refusal to recognize them due to shame, religious concerns, peer pressure, etc. Once they find themselves in a more accepting atmosphere for sexual exploration, they may come to realize that they have preferences for people of the same gender. This may include still having heterosexual tendencies (realization of bi-sexuality) or recognizing that they do not truly have sexual desire, or very weak sexual desire, for the opposite sex. And there you go.