In order to maintain a strong relationship over the long-term, always work on a project together. Raising a child is a kind of project, sure, but the kind of projects I’m talking about here are shorter-term and more varied. They could include remodeling a house, building a garden, writing a book, or launching a business. Physical passion may wax and wane over time, but working on an external project can create camaraderie, a sense of accomplishment, deeper communication, and personal growth. It’s fun to celebrate together when the project is complete. Also, shipping multiple projects over time builds both history and momentum within the relationship. This makes the relationship feel like something you’re creating together that keeps increasing in value, which is the purpose of having a relationship in the first place.