Adam Clarke on Judges 11:35

Thou hast brought me very low - He was greatly distressed to think that his daughter, who was his only child, should be, in consequence of his vow, prevented from continuing his family in Israel; for it is evident that he had not any other child, for besides her, says the text, he had neither son nor daughter, Jdg 11:34. He might, therefore, well be grieved that thus his family was to become extinct in Israel.