Take another line after Mike cuts back (7)
I believe the answer is:
remarry
'take another' is the definition.
(take another spouse)
'line after mike cuts back' is the wordplay.
'line' becomes 'ry' (abbreviation for railway).
'after' says to put letters next to each other.
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'cuts' is an insertion indicator (some letters cut their way into other letters).
'back' becomes 'rear' (synonyms).
'm' placed within 'rear' is 'remar'.
'ry' after 'remar' is 'REMARRY'.
(Another definition for remarry that I've seen is " Wed again".)