Boyfriend’s depression

My bf has been really down lately and the relationship has felt a little off because of it. I asked him today what was going on and he said he just feels depressed, and that he gets like this sometimes. I asked him what I can do to help and support him. He said he needs space and to be away from me, and for me to just not talk about it. I’m not trying to make it about me at all but I can’t help feeling like I’m part of the reason? We’ve been dating for a year and this hasn’t happened before. I also have really bad anxiety and ocd, I don’t want to tell him or ask him if I have anything to do with it because I don’t want him to feel like I’m making it about me, when something is going on with hin. I guess I just don’t know how to handle this sudden change in mood, and I don’t know how to be there for him because he’s not really letting me be there. I don’t want to just be absent, but I want to respect his wishes and not push him away. What can I do to support him but not be overbearing. I’m just really worried.