That doesn't really correspond to the reality of sexual behavior though. The mere presence of a partner and of a sex drive doesn't mean sex will be a desired outcome, since the traits of the partner in question are the determining factor.

Historically, a huge proportion of men have never reproduced and genetic markers imply a strong occurrence of polygyny (it is in fact still widely practiced today) In societies where status is comparatively more important and there exists a surplus of males, this is even more visible.

With basic income, selection would simply shift even more towards physical appearance and charisma than it does today.

Prize for the most un-classy comment of the month. Really, women are so desperate for sex that they have to have sex indiscriminately?

I think you may want to re-think this part of your worldview, nymphomaniacs exist but they do not make up the vast majority of the women, at least, not in my experience.

Not indiscriminately. In terms of sex, they go for the looks. Just like men.

Regarding long-term partnership and raising children, that's a whole different story -- just like with men.