I have to disagree. Saying that someone is homosexual or heterosexual in orientation does not mean they're exclusively so, as most people are capable of feeling some amount of attraction to either sex. It merely represents where their primary orientation lies, illustrating that it is lopsided toward one sex or the other.<quoted text>
They're bisexual. Enjoy sex with both men and women. It happens. They're not going straight to gay or gay to straight.
'Bisexual' is something of a misnomer, since few people are equally oriented on both genders. Most people I have found identifying as bisexual fall into one of two groups
1) Those who are really gay but not ready to admit it.
2) Those whose orientation is closer to middle of the spectrum than the polar opposites. They may still feel slightly stronger in their attraction to one gender or the other, but not enough so to classify themselves as gay or het.