I broke one of my front teeth in half, Why did my dentist drill down my two front teeth into little squares for Porcelain Veneers?

Porcelain Veneers are irreversible procedure, and require preparation of teeth ! I am sure your cosmetic dentist reviewed the pros and cons of having porcelain veneers for your front teeth.
Dental veneers require minimal removal of tooth structure so it can be substituted with porcelain, to change to your desired color and shape, as far as how much tooth structure is removed from your teeth, I can not see a photo of your front teeth preparation by your dentist, hopefully not much is taken off your front teeth, since then it would be called possibly a 3/4 or 7/8 dental crown.
The more discolored your teeth are the more removal of tooth structure is necessary to alter to a whiter color tooth. Also be informed that if the angulation of your teeth are not ideal, more tooth structure is required to be removed to place them in ideal angle.

The more conservative the dentistry, the longer your restorations will last you.
As far as temporaries, if they do not look even, or you have sensitivity, it is best to call your dentist so he can attend to those concerns, sooner than later.
Best of luck to you.

-- 
Dr Anthony Mobasser 
Reconstructive & Cosmetic Dentistry
9201 W. Sunset Blvd suite 618,Los Angeles Ca 90069
P : 310-550-0383