Married? Yes and sad by middle of the week, perhaps (9)
I believe the answer is:
wednesday
'middle of the week perhaps' is the definition.
I can't tell whether this defines the answer.
'married? yes and sad' is the wordplay.
'married?' becomes 'wed' ('wed' can be similar in meaning to 'married').
'sad' indicates an anagram.
'yes'+'and'='yesand'
'yesand' with letters rearranged gives 'nesday'.
'wed'+'nesday'='WEDNESDAY'
'by' is the link.
Can you help me to learn more?
(Other definitions for wednesday that I've seen before include "Day named after the chief god of the Germanic peoples" , "Sheffield side?" , "Fourth day of the week" , "See 1" , "In the oddly dewy Andes for the day" .)