This query can be interpreted in two ways: it could be a request for advice on navigating in long-term marriages, or a guide for creative writing/media analysis regarding mature female protagonists in fiction.
Mature romantic arcs often fall into these three narrative structures:
Ensure she is the driver of the romantic arc, rather than a passive participant being "pursued" or "saved." 2. Types of Romantic Storylines
This focuses on a wife finding a new romantic connection (often after a separation or emotional distance). The depth here comes from the emotional stakes —she has more to lose and more life experience to bring to the table.
To create a compelling mature protagonist, her identity must exist outside of her marital status.