After sex, your brain releases a chemical called oxytocin. Oxytocin is what bonds child to mother and partner to partner. So, your brain pretty much gets attached, hormonally, to your partner.MyEscapistUserName said:..what exactly does the brain do after sex that's so scary? I haven't heard anything except that it releases dopamine.crudus said:Just because you are sharing a bed, does that mean you are having sex? In my experience: no (...sadly). I really don't see the issue. Now having sex, that is a totally different issue entirely. Sex does crazy thing to your biologically that is actually quite intense. I was saddened when I learned nobody told me about that. Sure they told us about all the STDs, pregnancies, etc, but never mentioned what your brain does after sex which is probably the scariest thing on that list in my opinion.
http://en.wikipedia.org/wiki/Oxytosin [The Wikipedia article on oxytocin.]
Oddly enough, I learned of Oxytocin in Sex ed.