1. Philip is 58 and still lives at home with his parents. He doesn’t take care of himself. He still lets his mother take care of him. He’s tied to his mother’s apron strings
2. Rachel decided to break off her engagement to Ted. She realized he would always take his mother’s side in a dispute, and would always be tied to his mother’s apron strings

Compare to: under (someone’s) thumb. An apron is a piece of clothing worn over the front of the body to protect normal clothing from getting dirty, especially when cooking. The apron is tied on with strings. The expression tied to (one’s) mother’s apron strings usually describes an adult’s continued dependence on his or her mother.