Henry, I really am sorry for your situation. I have hesitated on replying to your question because I don't actually know how helpful my comments would be. In terms of diet I do not know the answer, but from all I do know about foods for a healthy brain, Paleo seems to be ticking many of the boxes.
I am 30 and spent 2005 - 2007 nightclubbing and probably took around 30+ ecstasy pills over the two years. I do not recall suffering acute depression before (though have always been a thinker and more melancholic in temperament), but in 2009 I had my first real storm, and over the last 3 years have become very aware of the horizon.
For me acute depression is like a dark cloud that appears in my head out of nowhere. The only way I can explain it to people is that it is like being dropped into an turbulent ocean, treading-water to stay afloat and trying to bail out the water with a bucket. People forget that the very means and tools with which one could use to get out of the storm are the very means and tools which are made futile by the storm.
I really do hope that the following comes across sincerely and without any presumption or arrogance, I just want to share how I personally manage my storms. Perhaps this may be helpful for you as you continue your journey to recovery albeit possibly too slowly for either you or I.
I have a few rules in place that help me during a storm:
I watch the horizon for the storm, and learn to know my triggers: Sleep and not eating enough calories is a big trigger for me. I find that if I have a crazy week I get into a cycle of eating less full meals, drink more coffee, sleep badly and this all compounds into each other until I have to force a break in the cycle. This is almost impossible to do once I am in a cloud of depression, so I have to make the effort to check myself regularly when I notice I am starting down the path. When I am at my weakest in this cycle, just a something small like a personal criticism can seed the storm and within days I can fall into the black.
I do not trust how I feel or what I think during the storm: Once I am in a storm, everything I say or think about myself I have to ignore. I have to find things that are objectively true outside of myself and hang onto them like an anchor; things that are unchanged, solid and remain no matter how I feel or think. I have to know these and have these at hand before the storm as my hands are tied during and I will not have the ability or desire to find them in the waves.
I do what I am responsible for: This is the greatest and hardest rule but the most effective for me. Simply it is to do what I am responsible for whether I feel like it or not. That means that if I don't feel like finishing the work I am assigned in my job because I feel and think I just cannot do it, because it's too much and I left it yesterday and so it's more; I just have to do it. That which is my responsibility whether I feel like it or not, I do that. I just start, just answering one email, and then another even if I have a hundred, just do the top one and then the next and the next. Before long I am brought out of myself, and into objective circumstances outside of myself. I try and schedule my work, then follow my schedule not my feelings.
I am sorry if perhaps you are trying to keep afloat yourself and I am just describing the water again, but I hope that I have been helpful even in just a small way. I really believe that the body and brain are incredible, far more incredible then we think. I believe that recovery is possible, it may take decades but Henry keep on keeping on. The Paleo diet that we are doing here from all I am reading and continue to read and learn about, appears to me to be a beneficially maximized lifestyle of eating, and perhaps we will never be fully healed, but perhaps closer then we ever could be if we were not making this dietary change.