Generally, many states require that you live separate and apart for the statutory period of time. It also means that the two of you have not co-habitated. In some states, like Maryland, it is a criminal offense. Cheaper then going downtown for dinner. Every state is different.
Some states believe that if the marriage is over, then lets move on.
Others believe that if you make divorce too easy couples will not try to work out their differences. Now for the big question, who should you hire and what will it cost. I must confess, you want someone like me. Someone who knows the law, will be your advocate, your knight in shining armor and your champion. While at the same time telling you what you can realistically expect so you can make the decision to attack or retreat, negotiate or litigate.