Should be noted the passages before and after 5:19.
5:15 Drink water from your own well - share your love only with your wife.
5:16 why spill the water of your springs in the streets, having sex with just anyone?
5:17 You should reserve it for yourselves, never share it with strangers.
5:18 Let your wife be a fountain of blessing for you, rejoice in the wife of your youth.
5:19 She is a loving deer, a graceful doe. Let her breasts satisfy you always. May you always be captivated by her love.
5:20 Why be captivated, my son, by an immoral woman, or fondle the breasts of a promiscuous woman.
Honestly I would recommend just reading all of proverbs 5 yourself; some high value wisdom about avoiding immoral women.