Terribly hot, also, myself: it’s horrible (9)
I believe the answer is:
loathsome
'it's horrible' is the definition.
(thesaurus)
'terribly hot also myself' is the wordplay.
'terribly' is an anagram indicator.
'myself' becomes 'me'.
'hot'+'also'='hotalso'
'hotalso' anagrammed gives 'loathso'.
'loathso'+'me'='LOATHSOME'
(Other definitions for loathsome that I've seen before include "gross" , "Disgusting, nauseating" , "Horrid" , "Hateful" , "15 [ABHORRENT]" .)