Monogamy, or lifelong pair-bonding, is not practised by any other primate I know of (I’ll accept correction on this).
We are an evolutionary experiment, at least in this respect, and the mechanisms and behaviours developed to cope with it are far from perfect.
The main difficulty lies in the rapid development of emotional complexity in women, and its slower development in men. Inevitable given the differing biological purposes of the two genders and the behavioural patterns they require.
When you add the mass of acquired behaviours known as ‘culture’, the whole things becomes a mess, because we are creating complexities our non-acquired, genetic behaviours can’t cope with.
We will either sort it out through the evolutionary process or we will go extinct. The only advice worth giving or listening to is ‘be choosy about who you have babies with.”