1] It has been observed in rat populations that, when population reaches a certain density, homosexual behaviors begin the arise. There is some speculation that it is an adaptation that allows sexual outlet without the warring that might arise from over-competition for females, as well as keep population growth down.
I'm not suggesting this applies to humans; I am simply pointing out that homosexuality as a phenomenon occurs in animal populations, suggesting it is not simply a cultural thing.
Also means it's not a sudden change just a few thousand years ago, as you were speculating.
2] The chemistry involved in attraction is a continuum, not a one/zero switch. In any population, you will find men who are dominant, and men who are submissive, and everything in between. You will find preferences for highly feminine body forms, and preferences for less feminine forms. Some men are demure and are attracted to strength, physique, and masculine traits.