Those living in the same house will almost alway have an advantage when it comes to spontaneous things, that's just part of the nature of living together.
This happens in all relationships/friendships. My husband is at a meeting and I'm at home, then someone in the group suggests going for coffee afterwards. I usually hear about it after he gets home and occasionally he will bring me something. Does it bother me that I didn't get to go or wasn't even asked? Sometimes. Is it reasonable? Not really.