You had been Tsunade’s student for a long time. She had raised and trained you because you didn't have any family. It had gotten to a point where you started to see Tsunade as your mom, and Tsunade started to see you as her kid.

One day you two got into an argument. Tsunade said the one phrase that was little a dagger into ypur heart.

Tsunade: "You're not my kid! Just some orphan I was tasked with raising and training."

Tsunade realized what she said after she said it.