Why does Ernaux's vacation in Spain continue to be a bitter memory as noted in the memoir, The Years (Ernaux)?

Ernaux describes an image of the woman in the photographs surrounded by her family in Spain. She sees in the woman's eyes a weariness which was not there a few years earlier. Spain, in particular this one trip to Spain, resonates with the woman forever as the place where she completely realized her own marital and sexual dissatisfaction. She recalls feeling mesmerized by a beautiful woman there, likely comparing herself to that younger woman, and feeling sexually unhappy upon hearing a woman in the hotel experience an orgasm loudly and openly. She also recalls the weariness of her family life even though she wanted to avoid hurting her two sons by divorcing their father. As such, Spain remains a bitter memory.