See - Common Law Marriage. Parties to a marriage may not just agree not to be married any longer, nor just walk away from each other. Until the marriage relationship has been legally terminated the parties continue to have legal obligations to the other - and each of the parties continues to have an interest in the property of the other. The continuing obligations of one to the other - and interest of one of the parties in the property of the other may be determined by the law of the state where either of the parties reside. The interest in the property of the other continues even after death, and the amount of interest is determined by the laws of the state where one of the parties resides at the time of death.
Divorce is absolutely necessary to terminate the relationship.
Divorce is the judicial termination of an existing marriage relationship. Annulment is a judicial determination that although a marraige relationship was attempted that no relationship existed. In an annulment the relationship is declared null and void. Grounds for annulment may vary from state to state, but generally grounds for annulment are based upon one of the parties not being legally competent to enter into the marriage. Fraud by one of the parties, and even impotency, may be grounds for an annulment.