Possible Clues:

• Fall apart — it isn't agreed (anag)
• Setter aiding anagram break up
• Girl's someone thankless about the heartless break up
• Go to pieces
• Agreed it isn't working, so break up
• Almost expose major-sounding collapse
• Diet's ruined with eating, eating recipe for crumble
• Detectives unite after breakup
• Smash, striding, with a tee shot
• Around top of grave unearth corroded decay