He developed severe anxiety in June, around the time his dog got sick, then his dog died in a matter of days, and my man spiraled into severe depression. Initially he was sharing his struggles with me but then got very distant and is now talking to me once every 1-2 weeks. 

It used to be easy to talk with him but since June it's very difficult to have any conversation with him. He gives one word replies and if my question is open ended, then he'd say something dismissive like "I don't know". And honestly I feel like he doesn't want to talk to me because now it is so "boring", though I tried to talk in all the supportive ways I could imagine (tried to talk normally about daily stuff, tried to ask him what he is dealing with, his thoughts, struggles, etc), but he just doesn't share anything. And also him not asking about me doesn't help, makes our conversations sound like I'm interviewing him, which I bet looks awkward to him now.

I'm so lost, I feel like because of us not being able to talk like usual he'll just spiral into more of "whatever, it's pointless, my gf doesn't even understand me". He's got into therapy and is diagnosed with GAD and depression since June, and it seems to be situational because for years I have seen him doing absolutely well, and he was nothing like he is now, it used to be so effortless to talk with him.

How do I make the dialogues work? What should I even talk about? I could just listen but there's nothing coming from him... Please help!