Getting married in spring, so tighten one's belt (5)
I believe the answer is:
skimp
'tighten one's belt' is the definition.
(I've seen this before)
'getting married in spring' is the wordplay.
'getting married' becomes 'm' (I've seen this in other clues).
'in' means one lot of letters goes inside another.
'spring' becomes 'skip' (skipping is a kind of springing).
'm' put inside 'skip' is 'SKIMP'.
'so' is the link.
(Other definitions for skimp that I've seen before include "Be niggardly" , "Act hastily" , "Use less than is needed, be penny-pinching" , "Cut corners" , "Spend not enough time and care on (job)" .)