I really like how the author created two realistic, imperfect characters. They're both in an unhappy marriage where both parties keep trying, communicating and putting in effort (to some extent) only to realise that in the end their wants are too different.
A lot of readers will demonize them for committinf adultery, which is fair. To me, it only shows that every individual relationship is different and that adultery, being ofcourse the ultimate betrayal of trust, isn't always black and white or an 'easy out'. You can't help but not blame them, even though it completely destroys their current relationship. Very well written and a lovely portrayal of realistic, human characters.