"All this while" means "Over the course of an unspecified period of time" but it doesn't fit at all with the part after the comma. In BrE, we usually say "All this time".
I've just discovered that I was born at 8pm. All this time, I've believed I was born at 10.32am!
Someone told me that brown really suits me and all this time I've been wearing nothing but red and black.
Interested in Language