It's horrible to conceal love for us (7)
I believe the answer is:
hideous
'it's horrible' is the definition.
(I've seen this before)
'conceal love for us' is the wordplay.
'conceal' becomes 'hide' (synonyms).
'love' becomes 'o' (love means zero in tennis).
'for' means one lot of letters go next to another.
'hide'+'o'+'us'='HIDEOUS'
'to' is the link.
(Other definitions for hideous that I've seen before include "Horrible" , "Unsightly" , "Extremely ugly" , "Ghastly" , "Extremely unpleasant" .)