Does it matter about me? Rather (8)
I believe the answer is:
somewhat
'rather' is the definition.
(I've seen this before)
'does it matter about me?' is the wordplay.
'does it matter' becomes 'so what' (I've seen this before).
'about' means one lot of letters goes inside another.
'sowhat' enclosing 'me' is 'SOMEWHAT'.
(Other definitions for somewhat that I've seen before include "To a certain degree - a bit" , "Rather, a little" , "Moderately" , "To a moderate extent" , "up to a point" .)