Adam Clarke on Proverbs 6:32

But whoso committeth adultery - The case understood is that of a married man: he has a wife; and therefore is not in the circumstances of the poor thief, who stole to appease his hunger, having nothing to eat. In this alone the opposition between the two cases is found: the thief had no food, and he stole some; the married man had a wife, and yet went in to the wife of his neighbor.

Destroyeth his own soul - Sins against his life, for, under the law of Moses, adultery was punished with death; Lev 20:10; Deu 22:22.