"Separation" in Virginia, also known as "living apart," occurs when a couple stops living together as husband and wife. When this happens, the couple is separated, even if they have not yet signed a Separation Agreement. Also, unlike many other states, Virginia courts do not grant "Legal Separations." The only things somewhat similar to this that courts can do are (a) "bed and board divorces" granted by the Circuit Court, and (b) orders saying which party gets to have exclusive use of the couple's home, often granted at the same time as initial temporary support orders.
The no-fault grounds of divorce that are available in Virginia are an intentional, permanent separation which is continued without interruption for one year, or for six months if there is a complete Separation Agreement and there are no minor children.
Separation Agreements, also known as Property Settlement Agreements, or sometimes by other names, are legal contracts that both spouses sign. In an ordinary divorce case or in a "bed and board divorce," these agreements can be used to decide any of the questions of custody, support, property division, debt and other matters which would otherwise have to be decided in a court hearing as part of the divorce. Most Separation Agreements deal with all of these issues. The Separation Agreement can even state that the divorce will be on no-fault grounds.
Separation Agreements also provide that when there is a divorce decree or other court order, the Agreement will be "affirmed, ratified and incorporated but not merged" in that court order. This means that the Separation Agreement can be enforced later in the courts as a contract, but it will also be part of a court order which can be enforced through contempt-of-court proceedings. Separation Agreements are binding, forever, for both parties, except that decisions involving the children, such as custody and support, can always be changed by a court at either parent's request. Reconciling is another exception.
Bed and Board Divorces are similar to "Legal Separations" which courts in other states and countries grant. They are rare and mostly used when people want to be legally separated but have religious objections to divorce. They also sometimes file for them while waiting to get grounds for a regular divorce.
If the Agreement was drafted by your spouse, your spouse's lawyer, or even by a mediator or lawyer/mediator who was hired by both spouses, you should have your own lawyer review it before you sign it.
If you resume living together as a couple, the Agreement becomes void, unless it includes a reconciliation provision that says it will remain in effect after reconciliation. Reconciliation also destroys any grounds for divorce based on the earlier separation or desertion.