Sex differences in reaction to a romantic partner's infidelity are well documented and are hypothesized to be attributable to sex-specific jealousy mechanisms that solve sex specific adaptive problems. There have been few cognitive-based investigations of jealousy, however. Here we investigated sex differences in implicit processing of jealousy-based information. In Experiment 1, we used the implicit association test (IAT) to investigate sex-differentiated biases in classifying sexual or emotional infidelity information as being positive or negative. Men made significantly more errors when asked to classify as pleasant, words indicating sexual infidelity. In Experiment 2, we modified the Stroop task to include words that depicted infidelity-related topics in three priming conditions: sexual infidelity priming, emotional infidelity priming, and a no priming control. Men were significantly slower to respond after being primed with sexual infidelity scenarios. The effect of sexual infidelity priming was not word-category specific, suggesting that cognition about a partner's sexual infidelity hijacks general cognitive and attentional processing. These findings suggest that men may automatically classify information about sexual infidelity as negative and that the automatic negative processing of sexual infidelity takes precedent over other types of immediate cognition.