It is just how women evolved. Men evolved to be a loyal provider to the mother of his children (because that gave his offspring maximum chance of survival). Women evolved to be DISLOYAL and ALWAYS on the lookout for a better provider (because that gave her offspring maximum chance of survival). Same goal, different strategies. Nature doesn’t care about ‘justice’.

Because they evolved differently, women do not need love the same way men love women. This is why women get over a long term relationship break up so much easier than men because they were never that deeply psychologically invested in the first place.