An Ongoing Mess

If after 2 million years of Human evolution most (!) men and woman still can't form harmonic and stable relationships (neither live happily with continuously changing partners) then this means:
a) that this is in fact the best reproductive strategy (i.e. semi-stable relationships produce the highest off-spring rate, due to adultery sex or serial monogamies).
b) that this is an obligatory negative by-product of another very favourable trait (e.g. the difference between men and woman, or individuals in general, allows specialisation into different tasks, which is important for a community).
c) that we have not yet adapted to our current condition (overpopulation and high mobility means extremely frequent encounter of attractive potential partners)
d) that the Gods like to have a laugh sometimes.