Bisexuality is the "mental condition" due to which one is
attracted to personalities rather than bodies. It's not some
backlash reaction to do with psychological or social trauma, as you seem to be suggesting. It's not
wrong. It's probably the natural state of affairs -
bonobos are bisexual, as well as
dolphins.
There is no point at which one becomes "fully homosexual", either. Never met a gay man who hasn't slept with a woman at some stage, myself, and I've met a few. By the same token, no one is entirely hetero. After two years of marriage to a "completely straight, double Y chromosome, red blooded farm boy", we've compiled quite a list of guys he would, and even arrived at some definition of what's his "type".Just a small personal example.
Your basic mistake is that you seem to have been tought that human minds have little drawers in them into which things like sexuality fit nicely, and people who do things outside the acceptable drawers simply have a messy mind. Well, they don't. They just have a different one. Like hair colour, you know? You wouldn't ask what trauma happened in a person's childhood to cause them to have green rather than brown eyes, would you?