It is complete, utter, BS to suggest that someone can change their sexual orientation!!! OMG...that's just... ignorant and stupid.
Yes, some people's sexuality is a little more "fluid" but that isn't the case for EVERYONE.
Gosh I even thought I was a bit weird for never ever having any sexual thoughts about females (given that sooo many women I speak to have experienced some attraction for the opposite sex) but seriously... I have realised that I could never become lesbian or bisexual. I just DO NOT feel sexual attraction to women. AT ALL. Thinking about it just...leaves me totally cold.
In fact, I always say that the only way I could become gay would be to turn into a man

. Yup, I reckon if I was a guy I'd be a raging homosexual!!
That being said, I think the same is true for lesbians and gays... if you are 100% lesbian you can't just change to be something you are not!! You may be able to have a sexual relationship with a man, but that doesn't mean you'll automatically be straight

.
Now just because one individual person has a more flexible sexuality, doesn't mean others do... you can't, and shouldn't, ever assume to know more about what one person is capable of doing than they do!!
Just...ugh...
Also...I might point out... don't you think that a lot of gay people haven't actually TRIED to convince themselves that they're not gay?? It's gotta be a heck of a lot harder being gay in our society than straight!! I've known people who have tried to delude themselves for years...have lived in hetero relationships blah blah blah... but one thing they've never actually managed is to actually change their orientation!! I mean if it was possible for gays to become straight, I'm pretty sure there would be a heck of a lot fewer gays out there, as most people would choose to be straight rather than deal with all the rubbish that growing up in a mostly-straight society, surrounded by judgemental people, entails.