Depression advice

I am 22F and my SO (24M) is suffering from depression and anxiety. Until two months back, it was mild depression but now he has been confirmed by his doctor that the level has changed to severe depression state. He drifted apart from me during these two months since I couldn't take care of him and now although he has returned back, I am doubtful on how to be helpful and take care of him. And this is a long distance thing. He already has a therapist and everything but his condition takes a toll on my mental health too. How can I support him in this tough phase while balancing my mental health too?