When I think "lifestyle", I think ... I'm not sure what I think. I think "Lifestyles of the rich and famous." I think of it as something that one can change at will, or something that can be changed with the help of a fashion consultant or with a change in income.
I don't think of it as a sexual preference. An expression of sexual preference, sure. I can be living a "lifestyle" where I'm getting it with somebody different every night, with bars usually involved. I can have a "lifestyle" like Hugh Hefner. But to say, "I don't approve of your lifestyle, but it's your choice," to one's single (and not getting any) gay college student son, and not feel that one's single (and not getting any) straight college student son has a "lifestyle" worth commenting on... that leaves me with the distinct feeling that the person using the word "lifestyle" is using it as a weasel word because they don't feel that "sexual preference" or "sexual orientation" is quite the thing.
I think that the reason that "lifestyle" used in place of "sexual preference" or "sexual orientation" is that "preference" and "orientation" both imply that it's something that is less likely to change, with the cause for the sexual orientation more because that's just the way it is (why do I prefer chocolate over coffee? Because.) rather than by a conscious choice of the person's.
I think that people have three or four settings on their sexual orientation. The first setting is probably hardwired into the brain; I read some article several years ago saying that there was some similarity between the brains of straight men and lesbians, where straight women had something different. This is the broadest setting.
The second setting is early development; I've read also that someone's psychological sexual preferences are usually mostly formed by experiences before the age of four or so.
Third is later conditioning and experience, where things that one might before have seen as attractive are labeled by experience as being bad, and things that one might never have before associated with attractiveness coming to be attractive because it's associated with other attractive things. Before the age of 15, I found long hair on men unattractive. After the age of 15, I started seeking it out. I used to find a certain casual disregard for the rules attractive. At the age of 23, I realized that due to some experiences (Shawn) I found it extremely unattractive. I do not believe that biologically heterosexual women can be "turned lesbian" by trauma; I do believe that biologically bisexual women formerly identifying as heterosexual can traumatically have their attraction to men turn off, and notice their attraction to other women in the absence of the overriding preference. This third layer can be tweaked around by counseling and focused self-mind-hacking, but no matter what the counseling does, the underlying biological and early psychological preferences are still present.
The fourth layer of sexual orientation, the choice of expression, is the only one that can be reliably consciously chosen by the person. I can choose whether I want to act on my desires. I can choose whether I actually go up and speak to the person I want to flirt with. I can choose to go to bed with someone I actually have no desire for. Having sex with someone, except for cases of rape, is always a choice. Choice can be affected by beliefs and other information. Sexual identity can be a choice. Before I knew that bisexuality was possible, I was still attracted to women from time to time, but chose to identify as heterosexual, because I believed that there was no middle ground possible between straight and lesbian, and I was more often attracted to men. When I learned that bisexuality was a possibility, I found that it more accurately described my orientation. Another woman believed that she was bisexual, but upon experimentation discovered that she had no actual attraction to women, and chose not to have sexual intercourse where there was no attraction, and afterwards identified as heterosexual. People can be pressured to choose a socially acceptable orientation; someone who would be bisexual but oriented primarily towards the opposite sex can choose to not act on the occasional impulses to interact romantically with the same sex, or be conditioned into thinking that all heterosexuals occasionally get the impulse to interact romantically with the same sex, and that it doesn't mean anything.
I do not believe that it is possible for someone who is biologically heterosexual to be "turned gay". Someone who is biologically heterosexual can become a part of the gay culture, and become just as fabulous as the Queer Eye for the Straight Guy men, but they will always be heterosexual and fabulous (I hate the term "metrosexual", but that means the same thing) and not actually gay. The supposed heterosexual clean-cut football hero who goes off to college and comes back flaming gay and also a drag queen? Never biologically heterosexual to start with. Culture and mannerisms and social mores are contagious. Biological orientation is not.
I believe that most humans are neither pure biological heterosexual nor pure biological homosexual, but anywhere on a sliding scale of biologically bisexual (pansexual?). Most are oriented more towards heterosexuality, and if the dominant culture is focused more on reproduction than hedonism, then the dominant culture will be heterosexual. It was originally, I believe, my mother or father's thought that when a culture experiences high population pressure, and expansion isn't an immediate option, there will be more social focus on non-reproductive forms of sexual pleasure; I would have to agree that this would make biological sense.