Help me understand my friend

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Hey adv!

A wall of text incoming:

Some time ago I joined a gaming server and made some friends there, including one rather specific guy. He is very intelligent and funny and we got close in a peculiar way: he confides in me, and I confide in him. He is not someone who opens up easily and the fact that he chooses to share some very intimate things with me rather than with his friends, or that he tells me about things he shares only with his immediate family is very flattering and means to me a lot. Likewise, I talk to him about my problems and personal stuff. So I think it's fair to say that we are friends, but... We almost never have casual talks and he is often distant and totally uninterested in interacting with me. From time to time I message him something I think can work as a good conversation starter, but our private convos are short and almost awkward. He gives curt responses or suddenly stops responding at all while still being active in the general chat. We rarely get to game together because usually when I'm free he is busy with his work, but even when it happens, it feels impersonal and weirdly official. Obviously it's still fun because he's a funny dude but I feel like there is some kind of tension or awkwardness that I don't have with other guys with whom are I'm less close in personal sense...
Can someone help me understand why casual interactions with this guy are so hard to come by and so difficult when they happen? Is there any way I can have more friendly interactions with him without being bothersome? Or should I just accept it for what it is? All help will be greatly appreciated!