The Arrangement by Sarah Dunn

Six months: no falling in love, no dating anyone that we both know and no talking about it with each other. That's the agreement that married couple Lucy and Owen decide upon. Living in an upscale Hudson Valley community with their son, Wyatt, they are secure in their marriage, yet are intrigued about the possibilities of being involved with someone else. When both Lucy and Owen start exploring their options, they find their relationship changing in ways they never expected.  The Arrangement is a highly entertaining yet believable novel similar to Tom Perrotta and Liane Moriarty's Big Little Lies.