Dater's plus one all over the place, with a leg on either side! (7)
I believe the answer is:
astride
'place with a leg on either side' is the definition.
I can't judge whether this definition defines the answer.
'dater's plus one all over' is the wordplay.
'plus' means one lot of letters go next to another.
'one' becomes 'i' (Roman numeral).
'all over' is an anagram indicator.
'daters'+'i'='datersi'
'datersi' with letters rearranged gives 'ASTRIDE'.
'the' is the link.
Can you help me to learn more?
(Other definitions for astride that I've seen before include "With one leg on either side, as sitting on horse" , "Passing across" , "Extending across" , "With legs stretched apart - tirades (anag)" , "Not side saddle" .)