Many clients are interested in obtaining a "legal separation." In Maryland, you cannot petition the court for a legal separation. You and your spouse can sign a contractual document or separation agreement that states that the two of you have agreed that you can live as though you are unmarried, which would be the equivalent of a contractual separation.
The court will consider you to be married until they have granted you a divorce.
For the purposes of divorce, you are physically separated from your spouse when you stop sleeping under the same roof and stop having sex.