Anna Karenina Part 5 Chapter 14 Page 9

He felt now that he was not simply close to her, but that he did not know where he ended and she began. He felt this from the agonizing sensation of division that he experienced at that instant. He was offended for the first instant, but the very same second he felt that he could not be offended by her, that she was himself. He felt for the first moment as a man feels when, having suddenly received a violent blow from behind, he turns round, angry and eager to avenge himself, to look for his antagonist, and finds that it is he himself who has accidentally struck himself, that there is no one to be angry with, and that he must put up with and try to soothe the pain.

Never afterwards did he feel it with such intensity, but this first time he could not for a long while get over it.