We lived together for twenty years in Arizona, but never got legally married, but I believe we had a common-law marriage. Does that mean I can get spousal maintenance?

No. Arizona law does not permit common-law marriages, and since you never married otherwise, the law considers both of you to be single. In situations like yours, other states have created what is called “palimony,” which allows spousal maintenance for people who never legally married. Arizona is not one of those states. So, people who live together for decades but never marry are not entitled to spousal maintenance.