Not faithful (8)
I believe the answer is:
disloyal
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">not faithful</span>' is the definition.<br/ ><span class="explanation-format__explanation">('disloyal' is the opposite to 'faithful')</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for disloyal that I've seen before include "Not faithful, treacherous" , "Deserting allegiance or duty" , "Unfaithful or unpatriotic" , "Treasonable or treacherous" , "Deserting one's allegiance" .)