Married? He's crazy to become engaged! (4)
I believe the answer is:
mesh
'become engaged' is the definition.
(I've seen this before)
'married? he's crazy' is the wordplay.
'married?' becomes 'm'.
'crazy' indicates an anagram.
'hes' is an anagram of 'esh'.
'm'+'esh'='MESH'
'to' is the link.
(Other definitions for mesh that I've seen before include "Undeviating" , "Net, snare" , "Entangle, entwine" , "Net fabric" , "Become entangled - become engaged" .)