That's not exactly the kind of choice we mean. Here's another way of looking at it:
We might envision the erotic potential we're born with as a shapeless mass of water. As we experience different things throughout our lives, we build dams or dig channels to direct the flow of that water toward certain types of people—people with certain hairstyles, certain personality styles, certain accents, certain opinions, and frequently, certain genders. Sometimes we make a conscious choice to build a dam or dig a channel; other times we blindly follow directions when our parents or the media tell us that greater happiness is to be found by directing the flow toward the opposite sex. At still other times, any emotional association from an experience we've had can provide the tiny ripple that starts the water flowing in a particular direction, and from there the water might even dig its own channel deeper without our help—for example, if you've had promising beginnings with several short males with green mohawks and nose rings (even if those relationships later ended badly), then when you get introduced to another short male with a green mohawk and a nose ring, you might quite possibly be more predisposed to feel affectionate toward or "at home" with him, or to immediately wonder as soon as you see him whether this might be your next promising beginning.
Now, at the particular moment that you meet someone you're attracted to, you may not have much choice about being attracted to them because in that one moment you probably don't have time to instantaneously reconstruct all the dams and channels that took many years to build. But if your reasons for having built the dams and channels in the way that you did become outdated, then over a period of time when the water level has subsided a bit, you might deliberately rebuild them in a different style—or you might unconsciously develop other emotional associations without ever really thinking about the fact that lately you're not so fixated on short males with green mohawks and nose rings as you used to be.
On the other hand, if you built your dams and channels to direct your attraction toward the same sex because your shared experience of the same gender role enables you to genuinely relate better to them in some way which is important to you, then even though you might consciously try to change and become more attracted to the opposite sex for the sake of social acceptance, your attraction to the same sex probably will not change—because the wish for social acceptance is an awfully stupid motivation for being attracted to someone, and something inside you must have realized this in order for you to feel same-sex attraction in the first place.