Hi, it's my first time posting but I've been reading all the really helpful threads that have rung a bell with me in my(new-ish) situation/marriage breakdown, so any more comments or advice will be very gratefully received. Sorry this may be a bit long...
In summary, my H was diagnosed with clinical depression in Sept 2010 which seemed to be related to many issues - sudden death of a close friend, mid-life due to H hitting 40, work stress, etc. He was signed off work for 3 months, put on A/Ds and started counselling once a week. He also started to go to the pub all the time and to drink far too much. I tried to be supportive and loving, although hard work at times, but H announced on 12 Jan after 11+ years of marriage that he didn't love me anymore, our marriage was over and that we should split up. 
I was gutted! It came out of the blue to me, I knew he had problems but I thought we'd work them out together. I have kept trying to talk things through with him, he says he doesn't know what he wants out of life and has been unhappy for 7 or 8 months, but much of what he says is contradictory and changes from day to day and week to week (I think due to depression distorting his view of life). H refuses to go to marriage counselling, says he is already getting counselling so doesn't need any more. I am so disappointed that he doesn't seem to want to try to save our marriage. I asked him right at the beginning if there was someone else but he said no. I've read all sorts of stuff on depression and saving a marriage and have eventually agreed with him that it would be better for him to move out for a trial separation. However, he's still not found somewhere else to stay yet, although he disappears off most weekends. Despite all this I have tried to remain strong and get on with my life with my very supportive rl friends and family (no DC involved).
But last night I found confirmation in his email (I know the login) of something that had been niggling at me. He appears to be having an affair with a woman he knew many years ago at school and linked up with again recently on Facebook, I think starting in in Sept or Oct. The email shows he was planning to look at houses on the other side of the country with the OW only 6 days after he told me wanted to separate! I now feel like I'm back to square one, totally heartbroken, feeling sick and lost. I asked him again last night if he was seeing someone else and he denied it again (but I know he is lying) he then lost his temper with me big time and looked at me like he hated me, saying all sorts of nasty things that just aren't true! I'm totally devastated and don't know what to do now - he stayed in bed and didn't go to work today and has just walked out the door without speaking to me (to go to the pub). I'm so sad :(, up to now I still had a little hope that we could sort his/our problems but I'm not sure if I can get beyond him lying and the way he reacted last night /today seems to indicate he's not even talking to me now. I know I will cope but I feel like I am still in limbo since he?s not actually moved out yet and is denying the relationship with the OW. Any suggestions for a way forward would be welcome!!!