The purpose of this research was to examine the relationship between relationship satisfaction, intimacy, monitoring of partner's behavior and jealousy, that is, happiness in relationships related to the use of social network sites (SNS). 308 participants between the ages of 18 and 30 took part in the research. The research was conducted online, and the instruments used were: Questionnaire about the participants' general data, Facebook intensity scale, Facebook jealousy scale, a scale that examined happiness in a relationship related to the use of SNS, a scale that examined the monitoring of partners' behavior, Relationship Assessment Scale and Miller Social Intimacy Scale. The results showed that there is a statistically significant positive relationship between happiness in the relationship caused by the use of SNS and jealousy on SNS. Furthermore, the results of the hierarchical regression analysis showed that monitoring the partner's behavior is a positive predictor, while relationship satisfaction is a negative predictor of jealousy on SNS. In addition, it has been shown that both relationship satisfaction and monitoring of partner's behavior are positive predictors of happiness in a relationship induced by the use of SNS. Finally, the mediating effect of intimacy on the relationship between SNS use and relationship satisfaction was tested, but the existence of such a mediating effect was not established. However, the existence of a mediating effect of intimacy on the relationship between gender and relationship satisfaction was established.