You must have support of course, when husband intrudes (4)
I believe the answer is:
thee
'you' is the definition.
(historical second person pronoun)
'support of course when husband intrudes' is the wordplay.
I cannot quite understand how this works, but
'course' could be 'e' and 'e' is present in the answer.
'when' could be 'e' (I've seen this in other clues) and 'e' is found in the answer.
'husband' could be 'h' and 'h' is found in the answer.
A single letter 't' remains which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
'must have' acts as a link.
Can you help me to learn more?
(Other definitions for thee that I've seen before include "You in the olden days" , "you many years ago" , "Poetically you" , "Quaker 'you'" , "Archaic form of 'you'" .)