A great way to manage couples and marriages is to use organizations, with people linked to them. This allows you to create work against them as a couple, such as a joint tax return. Here is an example of this.
John and Jane Doe are married. After setting them each up as individual people contacts, you can create an organization called "John and Jane Doe", and then link them each to that organization.
But if John and Jane were to ever divorce, the people would remain, you would just archive the organization. This way, you will still have access to documents and work associated with it.
Then, let's say John remarries and his new wife’s name is Jillian. You can then create a new organization, “John and Jillian Doe”, to keep track of this new couple.