It’s unbearable when, It’d be unbearable if, I can’t stand it when, I couldn’t stand it if
Structure
Verb［られる］［て］＋ては(1)＋かなわない
［い］Adjective［て］＋ては(1)＋かなわない
［な］Adjective＋では(2)＋かなわない
(1) ちゃ
(2)じゃ
(A) てはかなわない is an old-fashioned expression used to indicate the displeasure of the speaker/writer with (A). こう and こんなに are often used when (A) is an adjective.