In Virginia, you're separated when one spouse leaves the marriage with the intent not to return. That doesn't mean that one or the other of you has to leave the home, it just means that you make the decision not to live as husband and wife any longer. You're still married. You have to be separated for a year before your divorce will be granted, unless you either (1) can prove adultery (which qualifies you for an immediate divorce), or (2) don't have any minor children and have signed a separation agreement (then you can get divorced after a 6 month separation period). Separation is often a stepping stone towards divorce, though you don't have to get divorced just because you've separated. At this point, you can still reconcile or just live separate permanently.
Once you're divorced, the marriage is legally terminated. A marriage is legally terminated when a final decree of divorce is entered in the circuit court.