One planning romantic breaks with American husband (10)

'one planning' is the definition.
(a machinator makes machinations or schemes)

'romantic breaks with american husband' is the wordplay.
'breaks with' is an anagram indicator.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'husband' becomes 'h'.
'a'+'h'='ah'
'romantic' with its letters anagrammed with 'ah' makes 'MACHINATOR'.