Well, I think it's considered to be a good ending is due to the fact he's finally over Chase and getting the help he needs or at least working towards it.
from the TVTropes page: Chase makes peace with his ex, finds new love and escapes the town with the rest of his friends... but is still plagued by nightmares while Leo's life remains stagnant in Echo and he chooses to cut off contact with Chase entirely, although he is at least recovering from his obsession with their relationship