Musar for Arakhin 32:45

And it is stated there (Arachin 16b): "Why did the Torah single out the leper for 'Solitary shall he sit'? He [(by his slander, for which he was stricken with leprosy)] separated between a man and his wife, between a man and his neighbor; therefore, the Torah writes 'Solitary shall he sit, etc.' And R. Yehoshua b. Levi said: "Why did the Torah single out the leper for bringing two birds for his cleansing? (Ibid. 14:4). The Holy One Blessed be He said: 'He committed an act of prattling' [i.e., slander]; therefore, let him bring a sacrifice of 'prattlers' [i.e., 'chirpers']."

There are three types of uncleanliness: dead-body uncleanliness, zivah [genital discharge] uncleanliness, and metzora uncleanliness. The [one affected with the] first is sent only outside the camp of the Shechinah; the second, outside two camps, and the third, the metzorah, outside [all] three camps, as it is written (Vayikra 13:46): "Solitary shall he sit; outside the camp in his dwelling." That is, even the other unclean ones may not sit with him. And our sages of blessed memory have said. What is different about the metzorah that he sits alone? He [by his lashon hara] separated a man from his wife, a man from his neighbor — "Solitary shall he sit."