Just to veer off a bit, it's not always about hiding it or being closeted and posing as an orientation you're not either. Like I mentioned before, there are people that openly identify as gay and yet also have had or are in romantic/sexual heterosexual relationships (or vice versa) while openly identifying as gay. If a man's generally attracted to men and generally has no interest in women, but there's one or two specific women that they're attracted to, they might identify as gay completely reasonably.
Right. Like I said, one person who does that might consider themselves bisexual, while another might consider themselves gay with one or two exceptions. Or hetero with exceptions. Like Ianto in Torchwood: Children of Earth, explaining to his family that he didn't fancy men in general, he just fancied Captain Jack. Some people can fall for someone outside their normal preference and consider them an exception, rather than something that changes their overall preference.
Really, the research shows that very few people are purely one orientation or the other. Most people who favor one sex are at least occasionally capable of interest in the other. So it's really illegitimate to think of orientation in all-or-nothing or "one drop" terms. That's not how human sexuality works. It's more a matter of the overall, lifelong trend. And just about what identity you choose to associate with.