hmm... thinking about the caligula problem:
perhaps once aelius' leg heals up, and they are back in rome, aelius is guarding caligula's room and he admits that he listened in on aelius and spurius' first time together and begins to mock it, leading to aelius acting hastily and angrily (somehow, don't know how. you can decide that

) and spurius later has to help him think of a way to keep this under wraps (or not, because we could actually have caligula telling germanicus, and germanicus being a little confused/surprised at first, but eventually like "... alright...")