I often go for second round

Our brain is never satisfied

 

As others have said, and as has been seen with rat experiments, when we have one partner our sexual drive falls off quite quickly after sex.
But put in different rats/partners and the male rat will keep going until he is exhausted.
That is evolution saying impregnate as many different females as present themselves to you.
And of course porn is the ultimate source of a variety of females, accessible by a simple click on the mouse.
Sorry about the rat metaphor, but it is unfortunately true that we act just like rats in this area.

 

Three round’s sometimes, when I’m feeling really sorry for myself.