1) I've heard some people say that it involves ability to produce milk for the baby, and others say that it's a signal of health (ie evolution wouldn't concentrate resources there unless all the other organs were already healthy). I only mentioned the first possibility in this post, which on second thought was overly simplistic.

2) You mean in relation to the evo psych of lust? Yes, I suppose that's true; as I said, a lot of this post is based on introspection, and when I introspect about the sex drive I tend to think about the straight male sex drive for obvious reasons. I don't really know what kind of footnote I could include besides "And females also exist and also fall in love for stupid reasons sometimes", but if there's something specific which you think needs to be said I'll add it in.

(AFAIK, there's no good research or theorizing on the evolutionary psychology of how homosexuals select partners, and the evolution of homosexuality is still a confusing and controversial field. Would be interested if you know of anything.)