OK pretend for the sake of arguement that Hermione is at least 17 or 18 (she's still at hogwarts so she can't really be any older!). And that sirius isn't dead (obviously!)
The idea behind this video is that Sirius and Hermione have deep feelings for each other,which they try to ignore, but find it impossible.
Harry suspects there is something going on and resents the blossoming relationship between his Godfather and his best friend, as well as the fact they continue to lie that there is nothing between them.
I didn't really intend it as a love triangle, but if that's how you interpret it then that's fine too!! I was just trying to show that Harry was jealous of their closeness, and was feeling as if he were being pushed out of the way!
YouTube kinda murdered the quality on one or two clips!! sorry about that!!