OK we covered the biology of sex, which if I did my job, proved to be completely unarousing unless you have a major science fetish. If you do, then you’re welcome.
The thing with writing sex in your settings, with creating and understanding the sexuality of the beings and creatures in your setting, is that it goes beyond biology. Think of it as a continuity – the biology is just the start, but it leads to other things. Biology is the foreplay, if you want to dangerously skirt metaphors I have no intention of expanding on.
Once you have creatures reproducing, be they human or otherwise, once evolution kicks in (or the gods take charge or whatever) then you may have sentient creatures dealing with sex. That’s when things get a lot more complicated and less scientific.
Sex is part of our minds. For some of us, an extremely large part.
Now things get personal. Literally.