Carina is a joke of a character, always has been. Since Meredith and the man-child have broken up, it's her responsibility as the sister to take care of her brother and (literally) pick him up off the ground and get him the help he needs. She knows the deal, after all, since she's experienced it with their father. But she's too busy spending all of her time at the fire station gettin' busy.
But thanks for clarifying that which we already could assume!
Honestly, this Deloser diagnosis and spiral is just the show runner's way to try and give him some "dark and twisty" experience because apparently that will somehow bring him more equal to Meredith. Krista said that in no uncertain terms in some recent Deloser vs McWidow(er) love triangle article at TV Line. In any case, No. Suffering from a mental illness does not make an insecure twenty-something fifth year resident, never married no children, whose fallen hard for a multitude of women in a short amount of time (Maggie, Jo, Sam Bello, Meredith) does not make him any closer to being equal to Meredith Grey, Our Lady of the Sun, married, widowed, mother of three, award winner, Chief of General, has had multiple near-death experiences, etc etc etc.
Nice try, though.