I'm a her 2 stage 3 breast cancer patient my dr advice me to have zometa every 6 mos. Is zometa can help prevent bone metastasize? Is it helpful to avoid bone cancer?

Yes possible. Zometa is uses to prevent osteoporosis and it is not a chemotherapeutic agent . Its uses along with stranded chemotherapy , 41 % time it prevents or delays skeletal related events ( sre ) and 17 % of risk of development of metastasis.
Debatable. There is some suggestion that zometa may prevent development of bone metastases. But it is still not a standard of care because one study suggested a benefit which has not been confirmed in further studies. I will leave it up to the judgment of your oncologist and you .