My dental bonding chips very easily, why?

Dear BrittMH
Bonding can be a great cost effective way to repair a chip but the pressure put on teeth, especially front ones on a daily basis can cause the resin material in the bonding to chip off. 10 years is quite a long time for anterior bonding to last, in addition over time the porous nature of plastic bonding can stain. That said, it sounds like you may also be clenching your teeth (a very common cause of your type of breakage). I would suggest that you start off by wearing a night/biteguard. Your dentist can make you a custom fit one or for about $20 you can buy one at the drugstore. It won't be as custom or streamline as the one that your dentist makes but it will do the job. 
If after wearing the guard diligently your bonding still breaks I would suggest that you discuss the option of a crown or possibly depending on your bite a porcelain veneer with your dentist. Both restorations are far less conservative than the bonding as they both require the reduction of tooth structure. However, the porcelain used in these restorations is much stronger than the plastic and is far less like to break and won't stain like the plastic/resin bonding.

Just because you had braces in the past doesn't mean your teeth/bite are in an ideal position. Teeth will shift unless you're wearing a retainer everynight. 
If your bonding keeps chipping, you should wear a night guard and or retainers that protect your teeth but keep them in place.  The surface area of the bonidng might be too much or too little....I can tell for sure without a photo. You may also need a crown which is more invasive and costly but will not chip. If you crown a front tooth, crown BOTH front teeth for the best result.