Sexual desire contributes to overall sexual and relational health among long-term romantic partnerships. However, little research has examined the nuances of partner-level sexual desire and behavior on a daily level, despite evidence that it ebbs and flows and is more of a state than a static characteristic. Additionally, daily sexual behavior and desire may impact women differently than men. Therefore, understanding individual and partner-level dynamics among men and women may provide a more nuanced understanding of sexual desire as a situational state in the context of long term couples. A sample of 87 mixed-sex couples (174 individuals; M age = 33 years) in long-term relationships (M = 9.33 years) completed a daily electronic report for 30 days and reported on their daily sexual desire and sexual behavior. A series of four stability influence actor partner interdependence models were conducted to investigate the individual and partner-level link between men and women's daily levels of sexual desire and their sexual behavior and desire the following day. Findings indicated that daily sexual desire fuels sexual desire on the following day, particularly for men, regardless of whether sexual behavior was engaged in. Additionally, sexual desire on one day impacts next-day desire for partners, particularly on days when sexual behavior occurred. Contextual, partner-level contributing factors seem to have the largest impact on daily levels of sexual desire among long-term couples. Implications and future research directions are discussed.