Tenofovir had been in use for Hepatitis B for about 8 years. It was approved for use in HIV patients for much longer. It is generally agreed that TDF is safe and efficacious for HBV with no drug resistance reported so far. In some patients with previous history of kidney problem, TDF may cause a decline in kidney function, this can be handled by dosage adjustment. Consult your doctor. Reduction in bone density has also been reported for long term users.
Whether you have to use TDF forever is a moot point. Many doctors would disagree, stopping antivirals after a period of sustained response and consolidation is always possible for about 50% of patients. Furthermore, a cure is also likely in the not too distant future.