Clue: Small part of what comes next said you fell in love head over heels (5)
Answer: OVULE
Explanation: Definition: Small part of what comes next
An envelope ('fell in') of U ('said you') in OVLE, an anagram ('head over heels' – but does that suggest the required rearrangement?) of 'love', with a cryptic definition for an unfertilised seed or egg.