I'm appalled by the way this dishonest author writes about this topic. Sexuality throughout the teenage years is highly variable, and even more highly variable among the sub-population of most promiscuous people. It becomes more fixed with age, and numerous studies on teen-to-adult populations (longitudinal) have affirmed this. There's no "threat to" the fact it's a natural inclination anymore than your height changing over time is.

Examples of this include this paper and more recently this paper. Teenage years are exceptionally volatile in terms of promiscuity, sex, sexuality, identity in general. The author seeks to abuse this fact in order to undermine the fact sexuality is no more a choice than your height, and like height you grow into it as you mature.

Far more likely of an explanation beyond him pushing the antiquated Christian right propaganda of "hypersexual addiction", people finding out they're probably homosexual can experience a terrifying transition. This can include desperately seeking sexual affirmation by having sex with who they "should be" attracted to. I went through this, tons of gay men also went through this, and it's entirely driven by that same religious homophobia creating a self fulfilling prophecy.

Edit: To further drive this point home, individuals who identify as entirely homosexual have the same level of sexuality stability as those who identify as entirely heterosexual. Even from teenage years. Bisexuals were the primary unstable group, and that can entirely account for this data. See here.