The girl’s been stood up again and that’s tough (6)
I believe the answer is:
Here is my best explanation:
'that's tough' is the definition.
'the girl's been stood up again' is the wordplay.
'the girl's' becomes 'eves' (**).
'been stood up' is a reversal indicator (I've seen 'being stood up' mean this (in a down clue, letters go up)).
'again' becomes 're'.
'eves' written backwards gives 'seve'.
'and' acts as a link.
(Other definitions for severe that I've seen before include "Unsparing and uncompromising", "Taxing", "Very plain in style or appearance", "Austere, stern", "Harsh and exacting", "Very bad", "Strict, stark", "Harsh and stringent", "Extreme and difficult to endure" and "Drastic".)