The rest is details, and historically it ends badly for either or both, usually after the aforesaid offspring are toddling around.
Having said the above, once you get past all those urges (sooner or later), hopefully you'll end up with an opposite sex best friend forever that you can canoodle with, and if/when the canoodling stops, they're still your best friend forever.
Edited by hambergler, 02 November 2010 - 08:49 PM.