[header] How to live with a messy person [title] Allow the messy person to have their own area. [step] Contain the person's mess by allowing them to live as they please in their own space. Maybe the person has their own room and you both agree that they can be as messy as they want in their room. 
Or perhaps the messy person has free reign over their office and can keep it as chaotic as they'd like. [substeps] Make sure you both agree that the person's mess stays in the specified area and does not extend to the rest of the home.