According to Brehm’s emotional intensity theory (EIT), the strength of feelings of romantic affect towards a romantic partner should vary as a cubic function of increasing levels of relationship stress (i.e., deterrence to feelings of romantic affect). The study tested this hypothesis in a true experiment with 80 young adults actually engaged in a romantic relationship, by systematically manipulating stress, through a recall procedure, across four distinct levels of intensity (control vs. low vs. moderate vs. high levels of manipulated stress). As predicted by emotional intensity theory, feelings of romantic affect were strong in the control condition, reduced in the low stress condition (low deterrence), maintained intense in the moderate stress condition (moderate deterrence), and reduced, again, in the high stress condition (high deterrence). Findings and both theoretical and practical implications for professionals and future research are discussed, with special emphasis on how to promote partners’ everyday adjustments to stress and emotional intensity regulation.