Almost realise romantic acquaintance is unexciting (6)
I believe the answer is:
sedate
'unexciting' is the definition.
(I've seen this before)
'almost realise romantic acquaintance' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'realise' becomes 'see' (synonyms).
'romantic acquaintance' becomes 'date' (someone you're dating).
'see' with its last letter taken off is 'se'.
'se'+'date'='SEDATE'
'is' acts as a link.
(Other definitions for sedate that I've seen before include "Calm and demure" , "Tranquilise" , "Calm - staid" , "Quiet and dignified" , "Slow" .)