I want to leave my wife but we have a child. You have to be seperated for one year in SC to get divorced. How can I leave legally?

You need to petition the court with a complaint and summons and also file a motion for temporary relief.  At the temporary hearing the court can establish who stays in the marital home, child support, child custody, alimony (if any) and other issues that need to be addressed on a temporary basis. However, you must be separated before you can file, not that it would be abandoment, but because the family court will not have jurisdiction unless and until you are separated.  There are exceptions to this, but the exceptions are few and narrow.  I am assuming there is no exception here since you didn't mention adultery or abuse.  You are right about having to be separated for one year before you can get a divorce if it is a "no fault" divorce.  However, if the wife and you have a full agreement on all issues and property settlement you can go ahead and make that a court order.  Or you can wait until the year is up and do the settlement agreement and divorce at once.  If there is no agreement then a trial will have to be set and it will take more than a year.