He reflects her, she him. Bonding begins to take place, trust is established, etc., etc., etc., finally copulation takes place. Maybe the bonding sticks, maybe it doesn't. Perhaps they are so attractive that it's necessary to mate with many. Let's even say our imaginary couple think themselves so beautiful that they begin to keep score.
Sex becomes a game, a conquest, a popularity contest.
Even all of that was designed by nature. Eventually the so called 'normal' female will become pregnant. All of which is a numbers game to nature - being unemotional about life or death. The numbers will find their own equilibrium. As the man and especially the woman mature they feel their reproductive fruit dry on the vine.