Odontoid fracture back in may have been told it looks good now had ct scan and now he sayd unstable and deadly need surgery is this normal 3mons later?

Not uncommon: Odontoid fractures can be notoriously hard to get to heal. The fracture pattern is usually unstable and the blood supply tenuous. It is not terribly uncommon to follow a patient where there xrays look good, but a followup ct scan shows the delayed union. I would discuss the options with your surgeon and don't hesitate to get a second opinion if you are concerned.