After reading the introductory paragraphs of Chapter 21 of Therese Raquin, why does Therese pull away, and how long has it been since they were lovers?

From the text:

Laurent advanced a few paces without speaking, and took off his coat and waistcoat. When he stood in his shirt sleeves, he again looked at Therese, who had not moved, and he seemed to hesitate. Then, perceiving the bit of shoulder, he bent down quivering, to press his lips to it. The young woman, abruptly turning round, withdrew her shoulder, and in doing so, fixed on Laurent such a strange look of repugnance and horror, that he shrank back, troubled and ill at ease, as if himself seized with terror and disgust.

It was more than a couple of years since the two sweethearts had found themselves shut up alone in this room. They had arranged no love-meetings since the day when Therese had gone to the Rue Saint-Victor to convey to Laurent the idea of murder.