Will my group health insurance cover my partner, even though we're not married?
Check with your employer. A growing number of employers are offering domestic partner benefits, including health insurance, to the unmarried partners of employees.
If your employer does offer health benefits to your partner, but your partner is covered by other health insurance, you'll need to decide whether it's better to be covered under one plan or two. A major disadvantage of a domestic partner plan is that the health coverage your employer provides to your partner is taxable income to you on the federal level (but not always on the state level). You'll need to compare both the cost of each plan and the coverages they offer, taking into account the additional income tax you'll pay if you opt to be covered by only one plan.