What can cause sudden changes in sexuality from straight child to 18, 18-25 asexual, 25 now only attracted to guys, each happens over night?

Subconscious: Nothing makes our sexuality. But we can definitely suppress or ignore or not think about sexuality in any real or perceptive way for years on end. Burgeoning adulthood is a common time when young men become aware of their libidos and sexual attractions. One cannot often attribute any real perception during puberty. Being attracted to another human is a gift. Celebrate it.