Hope this helps.
Normally, veneers will remain bonded in place for several years. It is not normal for one to debond within 1 month. You need to call your dentist to schedule an appointment. Take the veneer with you to the appointment. Bonding is best to enamel. If your tooth was missing most of the enamel, the bond could have been weak. Patient movement during the bonding procedure could have introduced moisture and loosened the bond. It is not possible for me to know the circumstances at the time and offer more complete information. Your dentist is your best source of information.