I don't care whether monogamy is 'inherent' or not - if not, neither is wearing clothes, taking medicines or writing poetry. This part of the argument is pseudo-scientific special pleading.
In my experience of monogamy, the 'never-ending happy ending' is one that you create, together, deliberately, day after day, in the moments of connection, in between the bins and the dropped socks.
However, sexual fidelity is not a one-time deal - sign on the dotted line and never think about it again. It is a gift, given freely if it means anything, and given each time the question arises. Like making a happy ending, it is an act of will and of love.
Harder work perhaps than riding the head-rush of sexual chemistry - but, I think, far more satisfying.
