The Malcontent

M.C. Bradbrook on my favorite:

"Bosola, to the end of his final couplet adds four mysterious words which come from a state far on the other side of despair. 

"Let worthy mindes nere stagger in distrust

To suffer death, or shame, for what is just --

Mine is another voyage.  (5.5.127-9)

"This blank feeling of Lucretian chaos is as far removed from the Deistic 'atheism' of Marlowe as from the determinist stoicism of Ford. Bosola, the conscience-struck and bewildered slave of greatness, so dominates any presentation of the play that the loves and crimes of the House of Aragon seem but a background to his tragedy."

And, in a note:

"He is far more frequently present than any other figure: he unites the two  groups, and he is the first character to exhibit the symptoms of  melancholy which afterwards appear in the Duchess, Antonio and the Cardinal, and which seem to emanate from him."

If you ask me, Daniel de Bosola is the love interest.