Marsupial goes round me as a great lover! (5)
I believe the answer is:
romeo
'a great lover' is the definition.
(I've seen this before)
'marsupial goes round me' is the wordplay.
'marsupial' becomes 'roo' (short for kangaroo).
'goes round' indicates putting letters inside.
'roo' enclosing 'me' is 'ROMEO'.
'as' acts as a link.
(Other definitions for romeo that I've seen before include "suitor" , "Literary lover" , "Code word for the letter R" , "Loving youth" , "Latin lover" .)