omg so i had this thought right, and like sirius and james out on a aurors mission yoke and james casts his patronus, but its not a stag like usual. nope its (whatever you headcannon reggie having as his or like reggies anamagus) and james is frozen in shock cause he and reggie had been dating in secret for aaaaages now and like reg is in his last year at hogwarts so james is falling even more in love with reg cause he realises his patronus has changed to match regs meanwhile sirius is sooooo fuckin confused like my man has every theory going through his head trying to figure out who has stolen his best friends heart and its not until reg sends him a patronus message and he connects the dots. but he doesnt tell them he knows, oh no. he fucks with them as much as possible until it gets to like james just blurting it out.