Joanna Kramer (Meryl Streep)’s Timeline and Summary

Joanna leaves Ted and Billy.
She spends 18 months in California; amongst other things, she starts seeing a therapist.
Joanna returns to New York without telling Ted. Sometimes, she watches him drop Billy off at school from the coffee shop across the street. (Creeper!)
Joanna tells Ted she's back—and that she wants custody of Billy. He refuses.
After a nasty court battle, Joanna wins custody of Billy.
When she comes to take Billy home, Joanna realizes he already is home, and tells Ted that she's not taking Billy after all.