Here is the full list of all 69 Returning To Mia achievements.
Started the story
Used the "Panic button" once
Used a certain little red button
Used the "Angle button" once
Used the "Two in one" button
Talked to Vivian for the first time
Talked to Grace for the first time
Talked to Mia for the first time after two years
Flashback!
Talked to Cindy for the first time
Talked to Pete for the first time
Talked to Sebastian for the first time
Found out Cindy is Sebastian's daughter
Talked to Isla for the first time
Got rid of a bully
Found out Mia want you to stay
Gave good advice to Isla
Got to know Cindy better
Went to dinner with Grace
You relaxed!
Talked to Sadie for the first time after a while
Talked to Giselle for the first time
Went looking for Sadie
Thought about Mia
Thought about Grace
Thought about Isla
Thought about Cindy
Thought about Vivian
Met someone familiar
Became a "Spartan"
Relaxed AGAIN!
Remembered your past with Mia
Took Sebastian's pants
Had to change pants
Kissed Isla
Told Cindy the truth
Used the back door
Complimented Mia's costume
Admitted you have fantasies to Sadie
Spied on Ellie and Vivian
Accepted Simon's proposal
Refused Simon's proposal
Chose to stay with Mia
Chose not to stay with Mia
Helped Grace out
Told Cindy you are interested
Picked Mia over Sadie
Picked Sadie over Mia
Found a mysterious note
Lifted an EXTREMELY heavy box
Agreed to come to Giselle's office
Trained with Mia
Failed to dodge properly
Had to make a "difficult" choice
Got rid of the towel
Rushed to Sadie in a time of need
Got slapped, hard
Went inside with Sadie
Didn't go inside with Sadie
Didn't turn Isla down
Turned Isla down
Talked to Hope for the first time
Reunited with Sadie
Proposed to Sadie
Chose Mia forever
Ended up single
Found all four endings
Unlocked the gallery
Collected all other achievements