Idealization – a positive bias in perception of the romantic partner is common and usually helps sustain the relationship, but in case of closeness perception the negative bias might be a more secure option. The present study examined whether spouses are more inclined to be negatively biased about the characteristics of their relationship and whether sex and rejection sensitivity (tendency to overperceive and overreact to even slight or ambiguous rejection) might foster this negative bias even more. Based on a model for understanding the process of relationship functioning, involving two independent dimensions, closeness, related to high self-other differentiation, and intrusiveness, related to blurring of self-other boundaries, we conducted a study among 50 married couples. The results indicated that participants underestimated their partner's closeness and intrusiveness. Women were more negatively biased than men when judging closeness of the partner. Furthermore, rejection sensitivity was associated with more negative bias in Closeness. These results were discussed with respect to error management theory, and models of ostracism and rejection.