Adam, someone (FF I think) recommended "After the Affair" to download and read. I believe it is a good book.
I wanted to point you at some UK resources as well. Relate publishes a series of booklets for people dealing with relationship issues of one form or another. They are also pretty good. My W and I bought "After the Affair" (same name as the American book), and "Loving Yourself, Loving Another", which is about self-esteem and it's importance for successful relationships. There are a number of other publications that they put out, including "Staying Together" and "Better Relationships". These are good in that they use examples from UK couples. I wouldn't say that they are better or worse than the other publications recommended by HH members, just that they are available in the UK and offer yet another source of advice and understanding. They sell for about GBP15 or so. I don't know where you are based, but there must be a Relate office near you somewhere.
Dave
I was also thinking... Okay, you are also dealing with someone in a lot of mental and emotional distress. I battled with my local Mental Health Trust, and GPs. No-one seemed to take her condition or our situation seriously.
The following are organisations outside the NHS who offer resources and advice to people dealing with mental illness. If you already know about them, then good, otherwise they may be of use.
Rethink
(They gave me fantastic advice and documentation about how to get my wife help)
www.rethink.org
Mind
(Not as useful as Rethink, but good nonetheless)
www.mind.org.uk
Samaritans
(Not honestly sure how effective they are - I phoned and they didn't offer me much practical help except to listen to me whine and cry and moan about how my W was sleeping in another woman's bed that night. Still, if you need to moan and whine and cry,...)
www.samaritans.org.uk