Quite the unique origin you have there! So far, there are two leading theories to homosexuality which could quite possibly be coincided (both could happen in different times).
1. Actual Gene: you only have one older sibling, which means you shouldn't be shirking on your testosterone intake. You could possibly have the actual phenotype that expresses homosexuality; the environment only influenced it more.
2. Too many siblings: the more siblings you have, the greater of a chance to have homosexual tendencies. This is mostly due to the lack of testosterone you receive while still in the womb, a significant portion to complex physiology that is hard to explain. According to your sibling background, this would be the least likely.
Eh, I don't know what is it that made me gay, but I don't like it .-. I might as well ***** about it here because people don't seem to understand that most gay people don't want to be gay.
Currently, I'm in the closet to just about everyone besides a 2-3 good friends of mine. 1. I'm not flamboyant in the slightest, so others guys hitting on me would be virtually unrealistic because they wouldn't know I'm gay unless I told them :L. That's not really the bad thing about being gay, it's the next part.
Family, oh my god. I started college this semester, so my parents are continuously asking if I met any girls and whatnot, and they always talk about how such a good father I'll be for their kids. They constantly remind me that I'm the last male of my family and if I don't have a child, I won't carry on the name of my family. ****. My parents are super religious and frankly, I'm afraid they'll disown me if I come out to them. I don't know what I'm going to do. My father is homophobic which just makes it worse. He always makes slurs against gays and I just have to sit there in silence while he does it. My parents are the of parents that taught me by example, but on the wrong spectrum. They're close minded, super religious, un-accepting, racist, alcoholics, my mother does drugs, my father is sexist, I'm none of that. I can't come out to them because I'll be a shame to them.
Tell me people who think homosexuality is a choice, why would I choose this? I'm constantly stressing out everyday because I'm not going to live up to my parents expectations, I'll never make them happy because I won't do as they ask.
/rant
[EDIT] TL;DR The cons of being gay outweigh the pros significantly, so why exactly would I choose to be gay?