I do believe being gay/lesbian is not a choice and you are born like that. Why? I think it's "personal taste". You know what you want, except you might be strongly or not so strongly influenced by others (
here is a related example). Yes, in early periods or life (or even later or forever if you are easily to influence) others tell you what you should and shouldn't do, but later no matter how strong is the influence of others on you, you'll find out what you trully like (or even who you trully are) and you may accept what you war and deny the influence of others from now on or hide it from everyone because "somebody told me it's bad/not okay". Let's take a simple example, it's stupid, but I think I can explain it well: colours. For me at least, I was always told that as a boy I
must like blue. I hate it, I personally like black over all, but my parents are not okay with it saying it's the colour of death and it may give me depressions and other stuff, instead they strongly suggest me to like blue or at least another colour, green, purple, etc. Nobody ever told me I should like black, it came randomly from inside my mind. I think same stuff goes with being gay. Somebody tells you that as a boy, you
must like girls, but in your mind you will always like boys.
I consider we can choose a type of education, a religion, aspect overall, what you like to eat, what you like to wear but they are based on what is in your mind (and sometimes taste, ears or many other senses).