“To tie a bow around it would only make it uglier,” Mr. Frost said. “When people ask about my relationship status, I usually just say: ‘It’s complicated. I like my wife, I just can’t live with her.’”…

Separations are usually de facto, rarely pounded out in a contract, and family law is different state to state. But even long-estranged couples are irrefutably bound by contractual links on issues like taxes, pensions, Social Security and health care.

Divorce lawyers and marriage therapists say that for most couples, the motivation to remain married is financial. According to federal law, an ex qualifies for a share of a spouse’s Social Security payment if the marriage lasts a decade. In the case of more amicable divorces, financial advisers and lawyers may urge a couple who have been married eight years to wait until the dependent spouse qualifies.