What is the default for legal custody without an agreement?

I do not have a signed separation agreement but the kids live with me and visit their dad every other weekend. We have been separated for 6 months. Without an agreement in place, who has legal custody of the children? Is it by default both parents or does it default to the custodial parent?

Until an agreement or court order is in place you both have legal custody of the children and equal rights to physical custodial time.