By Gis and by Saint Charity, 

   Alack and fie for shame,

Young men will do 't, if they come to 't; 

   By Cock, they are to blame. 

Quoth she, 'Before you tumbled me, 

   You promised me to wed.'

So would I 'a done, by yonder sun, 

   An thou hadst not come to my bed. 

(4.5.63-71)

Ophelia is mad in this scene she had found out that her father died and her love interest who is man was the killer. 

Paraphrase
Take this son: it's about the loss of a maiden's virginity and a broken promise of marriage. Just like girls in almost any historical era, she's stuck: if she doesn't have sex with the guy, he'll dump her for being a prude; if she does, he'll dump her for being—well, not a prude.

Speaker: Ophelia
Speaking to: no one/in madness