I don't know why I didn't tell you

I don't know why I didn't tell you
 

which 1 says "i dont know why i didnt tell you"

no se porque no te decia o no se porque no dijiste

I don't know why I didn't tell you.
No sé por qué no te decía.

It could also be

No sé por qué no te dije

depends on context.

thanx guys
 

i appreciate that guys

Tomisimo's option
"no se porqué no te lo dije"
"no se porqué no te lo he contado"
Saludos :D

I don't know, Why didn't I know.

This sentence, I feel, the form correct's so,

No se, porque no te dije.

I believe, the form more correct in pronuntation it could be so.

Regards.