I find it really strange that no one else has brought this up yet, but maybe no one has the experience I do, so I'll bite...
Depression is a disease, likes Crohn's or UC or cancer. You know how your diet doesn't GIVE you Crohn's but sometimes your diet can make your Crohn's symptoms better or worse? Having bad things happen to you doesn't GIVE you depression, though a better or worse situation can make depression harder or easier to tolerate. A lot of the time we say, oh, I'm not clinically depressed, it's normal to be sad because I'm dealing with this disease/surgery/breakup/etc. Well, sure it's normal, but that doesn't mean that underlying that you can't be depressed also.
I'm 100% positive from what you've posted that you are dealing with textbook clinical depression. Many people in my life and my family have suffered with it and it's not hard for me to spot. It's been there before Crohn's, it's been there with you through Crohn's, and it's still there after surgery. I think it's really unfortunate that somewhere along the line the idea of surgery = relief from Crohn's got its wires crossed with the idea that surgery = relief from depression. There is a strong mind-body connection, but when you are suffering from real depression, which you are, you cannot cure it just by improving your CD symptoms.
I know you have had trouble with anti-depressants in the past and I sympathize because generally that is the quickest fix. I cannot advise strongly enough that you push through the NHS BS just as hard as you can until you start getting adequate treatment for the disease
of depression which quite frankly is far more severe than your Crohn's right now. That treatment can be talk therapy, medication, lifestyle changes, or most likely a combination of some or all of those things. No one here is going to be able to reason you out of it, you won't be able to reason your SELF out of it. You have to seek help. If you don't think you will be able to seek help because your depression makes it hard to do things, tell someone close to you that you feel you need help with your depression and ask them to help you stay on track with getting access to treatment. You CAN do it and quite frankly you MUST. You will find a lot of relief. Like surgery it won't be easy but I really believe it will make a far bigger difference in your life than surgery.
dx'ed UC pancolitis 5/12
past meds: asacol hd, VSL#3, apriso, rowasa, xifaxan, 6mp, cortifoam, pentasa, cimzia, canasa, butyrate, flagyl, cipro, prednisone, remicade, methotrexate, cholestyramine, cortenema
current meds: none!
step one: colectomy, end ileo 1/16/13
step two: j-pouch construction, loop ileo 5/1/13
step three: takedown sometime