What potions have I drunk of Siren tears,
Distilled from limbecks foul as hell within,
Applying fears to hopes, and hopes to fears,
Still losing when I saw myself to win!
The first  quatrain  begins the excuses the Bard needs to repair his relationship with the Fair Youth. 
 He begins with reference to “Siren tears”.  The following Wikipedia entry states; 
 “In Greek mythology, the Sirens (Greek singular: Σειρήν Seirēn; Greek plural: Σειρῆνες Seirēnes) were dangerous yet beautiful creatures, portrayed as femme fatales who lured nearby sailors with their enchanting music and voices to shipwreck on the rocky coast of their island.” 
 In other words an outside force tempted him. 

Sonnet 119