Make more exciting drink to entertain old flame (3,2)
I believe the answer is:
sex up
'make more exciting' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.
'drink to entertain old flame' is the wordplay.
'drink' becomes 'sup' (to sup is to drink).
'to entertain' is an insertion indicator.
'old flame' becomes 'ex' (a former partner).
'sup' placed around 'ex' is 'SEX UP'.
Can you help me to learn more?
(Another definition for sex up that I've seen is " Add spice to".)