I think Sugar was very much happy for Carm when she found out he's leaving - she's the one who told him "it's OK if you don't love this anymore". Since the beginning of the series going back to S1, Natalie has been worried that Carm hasn't really dealt with the pain of losing thier brother to suicide, or the pain from the household they grew up in together. So for her, she sees this as him finally deciding to face the traumatic parts of life that he's been trying to pretend aren't there.
Carm did say he wasn't leaving the restaurant right away, that he would stay until they got the $850K debt settled with Jimmy, so it's a pretty safe bet that Jeremy Allen White will still be on the show next season.