The causal relationships between pornography use, masturbation, moral incongruence, and mental health are poorly understood. While the link between problematic pornography use (PPU) and depression is well documented, the affective dynamics (i.e., emotional shifts over time) associated with pornography use and masturbation have not yet been quantified. Utilizing an Ecological Momentary Assessment (EMA) design, we measured the affective dynamics of mental health variables collected from 22 participants before, during and after pornography use and masturbation, and examined the moderating role of moral incongruence in these relationships. Participants completed an initial survey followed by a four-week EMA, capturing data on sexual activities and mental health variables. Bayesian hierarchical mixed-effects models were employed to analyse affective dynamics. Findings suggest that pornography use and masturbation were linked to changes in affective states that spiked both before and after sexual episodes. The magnitude of these state changes was greater in participants with high moral incongruence, who experienced increases in guilt, shame, loneliness, and difficulty thinking, along with decreased hedonic mood and perception of relationship connectedness, either before or after sexual episodes. Our findings signalled the potential for intermittent spiking effects in craving prior to sexual episodes, as well as potential evidence for ‘brain fog’ following pornography use in both low and high moral incongruence participants. Further, we discovered opponent process dynamics in the mood of high moral incongruence participants, providing a possible causal mechanism that may explain how PPU can lead to depression.