How one loves to get a letter sooner than expected! (6)
I believe the answer is:
dearly
'how one loves to' is the definition.
I can't tell whether this defines the answer.
'get a letter sooner than expected' is the wordplay.
'get' means one lot of letters go next to another.
'a letter' becomes 'd' ().
'sooner than expected' becomes 'early' (synonyms).
'd' put next to 'early' is 'DEARLY'.
Can you help me to learn more?
(Other definitions for dearly that I've seen before include "Extremely - devotedly - at great cost" , "With affection - at great cost" , "At a high price - with fondness" , "Very much; at great cost" , "paying for big mistakes like this!" .)