I would recommend 'The Great Gatsby'. Although not a traditional 'cuckold novel', it has elements of unrequited love and complex relationships. Daisy is married to Tom, but she has feelings for Gatsby. The love triangle and the sense of betrayal in a way can be related to the concept. It's a great starting point as it's a well - known classic with accessible language and engaging plot.
Maybe 'Sense and Sensibility'. There are relationships where there is a sense of unfaithfulness or at least the threat of it. The Dashwood sisters' experiences with love include situations where men are not entirely faithful or there are misunderstandings that could be related to themes of cuckoldry in a broader sense. It's also a good beginner's choice as it has a more light - hearted tone compared to some darker novels on this topic.
A Room with a View could also be considered. Lucy Honeychurch is engaged to Cecil Vyse, but she falls in love with George Emerson. The shift in her feelings and the situation it creates in the context of her engagement can be seen as having some elements related to the idea of cuckoldry. It's a novel that is easy to read and gives an interesting exploration of relationships and social norms.