Insurance agents look at a wide range of factors when they offer policy options to drivers, such as the physical location of a car, the number of potential drivers, the driving history of each driver and the number of cars in a household. They base discounts on various factors as well. For example, a policyholder might have taken out more than an auto insurance policy through one insurance company. As a result, they might receive a multiple insurance product bundled rate discount.
In Maryland, you might be able to add two cars at different address to one policy as long as you can prove that you have a valid reason for insuring the second vehicle. For example, some soon-to-be married couples often switch vehicles. That said, you should ask yourself at this point if adding your fiancé's vehicle to your policy is a wise idea. The better option for you both might be to simply add yourselves on each other's policies, respectively, as named drivers. After all, you and your fiancé are not yet married. A lot can go wrong and prevent a marriage from even taking place.
Additionally, different insurance companies treat these matters in different ways. Your insurance company might have an internal policy that doesn't permit the coverage because they require that you live in the same household. You might also move to a completely different address when you marry that, although still inside the borders of Maryland, is located in a geographic area where you must pay more for coverage. Married couples typically also receive greater car insurance benefits because married drivers are perceived as being more mature and responsible. If you wait to add your fiancé's vehicle to your policy "after" you're married, when he becomes your "husband," you might actually lower the total premium payments with a discount as long as you both have safe driving histories.
The best thing for you to do is contact your insurance agent. Your agent can give you the best advice based on that company's policies, your current policy terms and any additional details you provide related to your situation.