Homosexuality: inborn or developed?

Years ago, I have friends who I hang out with, who, for as long as I can remember have been gay or lesbians eversince I've known them. Gays are fun to be with and most often their antics make me explode into laughter. They've got this incredible sense of humor and I get doses of good laughs whenever they are around! While most lesbians I came across with are pretty much subtle or serious with their behaviors, they are fun too but they don't give me as much amusements as my gay friends.

Just recently, someone that we know who was married and have grown up kids came out in the open (came out of the closet - the popular adage!) and I am bewildered after all these years, he's in his 50's, turned out leaving his family and wanting to be with another guy. (BTW, decades ago, We had a lesbian driver who brought a woman with her two young kids into our house and she hid them in her quarter for days, afraid that we will fire her!)

Had he known this all along? Was he born that way? Or is it just an alternative lifestyle? I am not qualified to judge whether homosexual desires are inborn or developed but it does confuses me why or how on Earth men or women, after having families would eventually wake-up one day and declare that they want to be with the same sex! Can anyone shed a light on this? Do you know anyone who came out in the open?On the other hand, I've heard/read some homosexuals who chose to be straight because of their religion. So what is your opinion on this?