Become disillusioned (4,5)
I believe the answer is:
lose heart
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">become disillusioned</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for lose heart that I've seen before include "Become disillusioned" , "Become discouraged in cardiac manner?" , "Become despondent" , "Here's a lot to cause courage to ebb" , "Start to despair" .)