One of the reasons I wrote "Scholarship" was that I could not recall a book on the same subject, ie love and loss in a prep school. That sentence is of course an invitation for many to send me numerous titles covering exactly the same ground!
The nearest in feel is "The Custard Boys" by John Rae (former headmaster of Westminster School).
The Custard Boys is not set in a prep school, but it does hint at a relationship between two boys in their early teens set during WWII. The Custard Boys starts out as if it is some sort of gung ho adventure story. You soon realise it is not. Indeed it ends up being a powerful anti-war story.
Now I have awakened your interest, I gently have to break the news that it is out of print. However, I picked up a version second hand via amazon marketplace.
I found out about the book having seen an amateur film of the book shown on Channel 4 one Christmas. If you search for "The Custard Boys" on line, you will see various sites offering it for download in various forms. However, I urge you to support the original maker the Children's Film Unit by buying a copy from them http://www.btinternet.com/~cfu/prods.htm. Be warned, the quality is not the greatest.
Further research revealed that there was a previous version of the film called "Reach for Glory" http://www.imdb.com/title/tt0056397/ starring the iron jawed Harry Andrews as our young hero's father. This version is my favourite version if only because it maintains the hint of a relationship between the two boys. Looking on IMDb, I read that the satellite channel "Simply Movies" has shown it in the UK. Otherwise, http://www.ioffer.com/i/reach-for-glory-1962-dvd-harry-andrews-kay-walsh-145626037 offers copies for sale. I cannot vouch for the status of this copy and have not used the site. I would also warn that the cover below is a very inventive re-imagining of the plot, this takes place in Norfolk, not some bombed out inner city!
There are also a couple of classic French novels covering similar ground but these I will come back to at a later date.