This is a tough one, I feel for you. I had this with my ex-wife, she suffered with depression for most of her life. When she had bad periods of it, she couldn’t communicate at all. Her eyes were just empty, nothing came out of her mouth. In her words, she was just sitting at he bottom of a big black hole looking up, couldn’t get out or be heard by anyone. People with depression often push people they love away, or take it out on those they love around them. She tried CBT but didn’t really engage with it, she did get better, but it was always there in the background and led to other issues. She switched off from me and concentrated on work I honestly thought I could pull her through it. I was a very difficult and heart braking relationship, eventually after a period of working away from home everything collapsed.
Its sad, but in hindsight I wasn’t happy either and it was getting me down. I lost contact with a lot of friends because she didn’t want to know them (life long friends, the people who would drop everything to pull you out the shit), my social circle fell to bits. She’s a lovely girl, but she will never be happy. I now see it as a lucky escape. Some people will always be like this and its draining, I had nearly 10 years of it, the divorce came through today. There is no easy love, Hope your Ok pal