Is it possible? Yes. Shifts in personality, desires, etc. can happen for a number of reasons. People have had head injuries and had shifts in sexuality, including a heavily increased/decreased sex drive or shift in orientation, as a result. Sexual traumas, particularly on children, can have lasting effects on their sexuality and sexual development both before and after adolescents, possibly (likely even) including homosexual behaviors where it may not have happened before... though that's obviously not possible to know for sure. And to a lesser extent, situations like long term isolation, desperation, abuse, or social pressure can make people more likely to act in ways that wouldn't have before as well.

Is any of that the norm or common for homosexuals? No. First, none of those situations is likely to result in a mentally stable, well adjusted adult that simply has attractions to the same sex. Those shifts in sexuality are likely to be just one of many symptoms of those traumas, most of the rest of which will be notably aberrant behaviors or traits. Second, the majority of people who have same sex attraction, whether exclusively or in addition to opposite sex attraction, have similar stories about being interested in the same sex from the time they first began to have any such attractions. Whether there is some genetic, developmental and/or environmental component that differentiates or influences ones sexual interest is not really clear. What is clear is that those interests seem to be largely set by the time they begin to manifest and be expressed in adolescence.

I don't think it's possible to 'become gay' save through some sort of change to the brain eg head injury as described below.

If you're straight, flip the question, when did you choose to be straight? Of course, unless you're in the closet, you never chose that, it's just the way you are wired.

It is possible to become gay by surgery. I have a friend who did that. He went into the surgery as a straight guy, and she came out of it as a lesbian.

In bisexuality there is the idea of "compulsory heterosexuallity" where a lot of people look at themselves and identify as straight because they have been trained to ignore their attraction to same sex partners because to chose otherwise is punishable. It's theorized that bisexuality might actually be more common than heterosexuallity and lead to the idea that geing gay is "a choice" because for a bi person it kind of is.

But for gay or hetero folk it is like trying to eat a food your palette finds disgusting. Like if you absolutely hate olives and keep forcing yourself to eat them you might get better at ignoring your sense of taste while eating them... But you will never get to the point where you initiate the neurological flip to where you actually enjoy it. While enjoying more bitter foods is just a function of aging up at some point certain things unique to you are hardwired in.

If you try hard enough, you can become anything you want.

But on a more serious note. We don't know. It's the whole nature vs. nurture debate and there are no clear outcomes.

But, as for I am concerned, you can be anything you like. Just don't bother me with your choices. If it makes you feel good, than good for you.

I have a male acquaintance who said he deliberately chose to make himself bisexual (from straight). But I'm not sure what methods he used; and I've heard other folks say he was probably pretty bi before this purported self-modification.

Realistically, no. Your just kinda born that way. You might not be aware of your sexual identity but it's in there. Some people take years to "come-out" to themselves. Often there's denial from years in internalized homophobia.

Same sex attraction isn’t a choice, but if you’re asking whether one’s sexuality can change by itself over the course of a lifetime, the answer is yes, but it’s not very common. I was straight, but sometime in my early 30s, started being attracted to women as well. I was not “always bi,” as some people claim must be the case in these circumstances. I had interrogated my sexuality quite thoroughly in an open and accepting environment years ago and found I was straight. It just…changed.

I guess it means on what you define "become."

I think it's definitely possible like that some just don't know they are, but become curious at some point and try. I think that probably happens less now though, since access to porn is so easy for younger people these days, there's probably not a lot of people that are unaware by say, age 20.

I know people experience things differently, but I went through a questioning period about being bisexual. Turns out nope, I'm straight as they come.

If you try hard enough, you can become anything you want.

But on a more serious note. We don't know. It's the whole nature vs. nurture debate and there are no clear outcomes.

But, as for I am concerned, you can be anything you like. Just don't bother me with your choices. If it makes you feel good, than good for you.

A lot of gay people state that they were born that way. OK, fine. I'm not going to argue that, but when many gay people also try to "turn" straight people into being gay. So how does that work?? That's like having your gay cake and eating it too.

It is more likely for women than it is for men - male sexual orientation tends to be more fixed. Men who "become gay" were likely always predisposed to it or bisexual at the very least. The causative biological mechanisms for male and female sexual orientation are different, and in the case of women, less clear