Help me find this movie

[YoshiMe]

So, several years ago my father watched this movie, and I stuck around and watched it too but I was too young, like 8-11, so I have no memory of actors and things like that, but I do remember the some of the plot, it's a movie, british I think, but I'm 100% sure of that, about this teenager in a mental institution talking to a journalist or doctor (female, I believe) about how he ended up there, the movie is told mostly through flashbacks, about his life at school, and how he met this other guy at school, who was kind of a loner and weird, and they became "friends". This loner was a little obsessed with him, something to do with how their fathers were both part of some secret order or something like (I'm not entirely sure if that was a real thing in the movie or if it was the loner's delusions) and one thing I remember clearly is him (the loner) claiming to be the "Pike", in reference to the suit of spades in playing cards. Anyways, the MC had a crush on a girl from school, and she fell down some stairs and died and it was kinda implied the loner guy killed her? Eventually the loner guy dies too, and I think the MC was arrested and eventually put into the mental institution because of those deaths, but the journalist or doctor manage to get him free. The movie ends with him on a train, and it's implied that the girl's bones are in his briefcase/luggage. Sorry, this is a mess, my memory really sucks sometimes, but I hope someone out there can help me find this