You're presenting a false dichotomy, heterosexual men never had men as "eligible" partners and them could simply not engage in long term partnership as opposed to change sexuality, but you've always been a poor poster who plays obtuse when called out on half cooked arguments
Your argument suggests we're frozen in time, it suggests the way people have identified and paired yesterday will be a constant and a predictor of how people will identify and pair tomorrow.
There's a growing population of men who call themselves heterosexual but engage in sexual encounters with other straight men, an idea that isn't in line with contemporary societal norms but also isn't unheard of as we can look as far back as Ancient Greece to find similar examples.
If modern society continues to implicitly push the idea that only virgin women are worthy of companionship while simultaneously encouraging the sexual liberation of women in a context where a different standard applies to men, a foundation is being laid that leads to men only using women for sex and concluding that's it's not an indictment on their masculinity it sexuality to seek companionship with the only population that doesn't get a bad reputation for having sex with multiple partners, other men.
, because they can't find women the right woman is jumping to a conclusion to say the least.
I think 18-22 the average woman has more bodies than the average man, then it starts to reverse in the mid 20s when men start leveling up. 18-22 are women's prime years in terms of sexual value. That's why men should spend their 20s bossing up and smashing women then maybe start settling down no earlier than their early 30s. Women want to take advantage of their sexual value in their prime years so men should do the same in their prime years.
what body 
