YOU SAID:
I can't believe you let me down
INTO JAPANESE
私はあなたが私を失望させるなんて信じられない
BACK INTO ENGLISH
I can not believe that you disappoint me
INTO JAPANESE
私はあなたが私を失望させるとは信じられない
BACK INTO ENGLISH
I can not believe that you disappoint me
Okay, I get it, you like Translation Party.