If you are legally separated, some companies but not all, will not make you list your spouse. If you are not legally separated then you will need to list your spouse but they can be excluded which means they will not be covered to drive on the policy and being married typically lowers your rate. Keep in mind, each company is different. Some will not let you exclude your spouse but most will. Your rate can be lower if you're only using your vehicle for commuting - but it varies. If you don't use your vehicle very much, you should consider a usage-based insurance program.
Good luck and if you have any questions, don't hesitate to ask