Hero’s boyfriend died in comparatively poor surroundings (7)
I believe the answer is:
leander
'comparatively poor surroundings' is the definition.
The definition suggests a singular noun which matches the answer.
'hero's boyfriend died in' is the wordplay.
'hero's boyfriend' becomes 'leaner' (I can't justify this - if you can you should give a lot more credence to this answer).
'died' becomes 'd'.
'in' indicates putting letters inside.
'leaner' enclosing 'd' is 'LEANDER'.
(Other definitions for leander that I've seen before include "Heroic lover" , "Learned like Hero's lover in Greek legend" , "Ill-fated lover" , "Hero's lover; rowing club" , "He swam for love" .)