Matthew Poole and continuators on Proverbs 5:18

18. Let thy fountain be blessed : and rejoice with the wife of thy youth .

Thy Wife, as the next clause explains it.

She shall be blessed with Children, for Barrenness was esteemed a curse and reproach, especially among the Israelites. Or rather, she shall be a Blessing and a Comfort to thee, as it follows, and not a Curse and a Snare, as an Harlot will be.

Seek not to Harlots for that delight which God alloweth thee to take with thy Wife. So here he explains the foregoing Metaphor, and applies it to his present design.

Which thou didst marry in her and thine own youthful days, with whom therefore in all reason and justice thou art still to satisfie thy self, even when she is old. Or he mentions Youth, because that is the season in which men are most prone to unclean practices, against which men are commonly fortified by the Infirmities of Old Age.