To drive your wife's vehicle, you should need to be listed on her car insurance policy as a driver; you do not have to buy your own policy.
Your wife should have already listed you on her car insurance policy. North Carolina auto insurance companies usually require that all licensed household members be placed on it as drivers. If she has not informed her insurance company about you as her spouse she needs to do so now and add you to the policy.
Once listed as a driver, it would be up to the guidelines of your wife's insurance company if you will be rated as an occasional driver, primary or secondary driver since there is only one car in the household and she is the primary driver of it.
You would not normally be able to get your own car insurance policy on your wife's car even if you wanted a separate policy; duplicate coverage (two policies on the same vehicle) is almost never acceptable by car insurance providers. Dual coverage would be confusing (whose policy is primary, etc.) and unnecessary since you should be listed on her policy.
If you have a bad driving record or there is some other reason you have not been listed on your wife's car insurance policy up to this point, then her rates may go up when she puts you on there. If this happens, shop around for more affordable auto insurance.
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