Though it seems that Kieran may initially have left Evelyn Bay for his own good, when we watch his behavior around his parents it almost seems possible that he really felt he needed to leave for their good - so they did not have to see him or deal with him on a daily basis - especially since his father for certain blames him for Finn's death, and his mother, by her silence does as well. Leaving, however, has helped him, and through therapy he has learned ways to cope that allow him to return, to overlook their judgment, and help them prepare for their move.
Here Harper again uses irony so well - Verity, Kieran's mother's name, means truth. How long has she dealt with him in a less than truthful or honest way. As acstrine says above, she has withheld so much from him for far too long.