..it's because you're not an asshole.
Vibes dude, but it sounds like you're still in a bit of shock. I think about this a lot, if lost one of my roommates at this point, I don't think I would know what to do with myself and it would probably take a while to even set in. I guess the only advice I can give you for not having to face something like this yet is to live your life in their name. Use the things that they taught you about yourself to you advantage and turn this into an experience that will make you a better person.
Stick close with your friend group too, it sounds like they need as much support as they can right now.
"Being serious about being serious is seriously serious ... take note and hopefully the serious skiing world will not cave in on itself."