Can someone become asexual

Yes, in a sense. Human beings are not capable of asexual reproduction in the biological sense, but asexuality exists as a sexual orientation. Just as bisexuality in a biological sense (one that possesses both male (pollen-producing) and female (seed-producing) parts) is different to being "bisexual", asexuality in humans does not mean the same as its biological definition.

Asexual people do not experience sexual attraction to any sex or gender, but can still experience romantic, aesthetic or sensual attraction. Asexuality is believed to apply to about 1% of the population, some of whom are unaware that it exists, and is not related to low sex-drive, hormone levels or mental disorders.