Toby's Room - by Pat Barker

I went straight on to this book - my next book club selection - as I have been travelling. It was nice to get back to fiction and a book of more manageable size. Here is the blurb:

When Toby is reported 'Missing, Believed Killed', another secret casts a lengthening shadow over Elinor's world: how exactly did Toby die - and why? Elinor determines to uncover the truth. Only then can she finally close the door to Toby's room. Moving from the Slade School of Art to Queen Mary's Hospital, where surgery and art intersect in the rebuilding of the shattered faces of the wounded, Toby's Room is a riveting drama of identity, damage, intimacy and loss.

The story is told from various viewpoints, but is largely focussed on Elinor and her feelings about her brother's death. Overall the story is quite well written and the pace is good. In a few places we are told something twice [e.g. Toby's "encounter" with the stable boy.], but, for the most part, there is attention to detail. I always like to feel that I have learned something when I read a novel and, in this case, I appreciated the background details of the war, life in the UK at that time and the medical practices.

There was one aspect of the book that I did not understand. We are clear that Toby was homosexual or bisexual, which led directly to his suicide. From a 21st Century perspective, his situation is hard to visualize. I am wondering why, at the beginning of the book, Toby has sex with his sister. I know of no connection between homosexuality and a tendancy to commit incest. This event does not seem to contribute materially to the story, so why was it included? Is it a red herring to make us wonder about his death?