my lug nut bolt broke on my rear wheel as i was removing my wheel...

i have a 2003 G35 coupe with 19k miles is it still covered underwarranty for this problem?

In my opinion, they should cover it. Seeing as how this is the reason why your wheels stay connected to the car. They shouldn't complain, lug bolts aren't expensive and are very quickly replaced.

You should think about changing all your lug bolts. Barring extreme abuse, your lug bolts should not break. If one broke, it wouldn't be out of the ordinary for that batch of bolts to have been produced to substandard quality.