niye bunca zaman demedin de başımıza bunca işi açtın

what does bunca zaman mean?

According to http://www.turkishdictionary.net/?word=bunca this means "for such a long time".

My try as learner would be:

Why didn´t you tell me for such a long time, and brought so much trouble on me?

A small contribution from me

huh interesting

yardım ettiğinizi için teşekkür ederim 

Argh, yet another stupid mistake  But many, many thanks Gokuyum for pointing it out