Victims of sexual abuse become aware of sex and sexual attraction, usually from the time that their abuse begins. Kids as young as kindergarten have been found to fantasize about sex or try and perform sex on their classmates as an attempt to make friends because the abuse warps their perceptions of friendship, intimacy, and social dynamics.
Even without that, the social norms of non-sexualized boyfriend/girlfriend relationships start young and some kids will definitely feel themselves pulled more towards one gender than the other, and this may or may not reflect their later sexuality. It isn't impossible to be "gay" that young, just that being gay means something really different pre-puberty.
Being shoved into gay clubs and living a "drag" lifestyle is probably sufficient to warp Desmond's perceptions of life and social dynamics bad enough to where he has likely associated sex with friendship from an early age. Notice he doesn't spend time with kids his age, only adults; he won't have a normalizing process that friends and other family structures can have. Isolated kids are highly vulnerable and easy targets for pedos because their sense of trust never matures past "mommy and daddy are god".