How do I help my boyfriend and give him his space and not take it personally?

My boyfriend when he’s really down pushes everyone away. I mean everyone and if he does respond he’s not the person he normally is. He warned me he was like this in the beginning and it doesn’t happen often. This time seems to be the worst. We’ve been together a year and a half and this has only happened 2 times. I want to help him and honor his wish. I know he loves me. I just wish I could understand his need for space from his loved ones. And what can I do for him while he’s like this?? And how to not take it personally??