Rashi: In the end, you will groan.

Malbim: In the end, when your flesh will be consumed via completion of lust, which consumes the flesh, you will regret your past.

Malbim (according to Melitzah): When he will come close to his end, when the flesh and its desires (due to which he veered from foundations of Emunah, in order to fill his flesh's desire) cease, he will groan and regret. He will think about the eternal world that he lost via the strange woman (heresy). One who girds his loins with Emunah, he does not worry about the finishing of the flesh, for he hopes for life of the Nefesh.

Lev Eliyahu (Shemos p.160): After death, when the flesh rots, "veha'Ru'ach Tashuv El ha'Elokim Asher Nesanah" (Koheles 12:7), you will need to give an accounting of all your deeds. Then you will scream about yourself - what did I do?! Why did I make everything Hefker (forfeit attributes) forever, for pleasure of a moment?!