Date exclusively (2,6)
I believe the answer is:
go steady
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">date exclusively</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for go steady that I've seen before include "Keep seeing each other" , "Court romantically" , "Date one person regularly" , "Have relationship as regular boy or girl friend - sounds stable" , "See someone regularly" .)