There will be an opportunity to tell Matt about the Julian thing in the next story update. I haven't written that conversation yet, but Matt definitely won't be a fan of Julian after that. Which will be a little awkward considering they're in the same classes and will be acting opposite each other in productions!
There will be other points like that where characters will react differently towards each other based on what they know. I don't know how crazy I'll go with the reactivity in that regard, but for Matt specifically, it makes sense for him to feel protective of his best friend.