I really wish I could answer that for you.
I have suffered what I have heard called "Diabetic Blues" by a doctor once for many years. I wake up some mornings and wonder why me? Why was I born with it? I have had diabetes since birth and really don't know anything else so I can only imagine what it must be like for people to be "normal" one day and diabetic the next. Please don't think I used the term normal as derogatorily.
I do get absolutely fed up having to stab fingers and inject every day - can I get over this..... not really. My way of coping is to disappear away into the game of World of Warcraft and kill some characters and before long I have forgotten what I was feeling bad about.
Unfortunately back in 2004 I went through a terrible family split where I no longer talk to or consider myself as having parents or a brother or sister. I became clinically depressed and have ended up on the max dose of medication for this. I have really good days as you mentioned then I have bad days. I attended a counselor through a free company called RAMH - don't know if this is UK wide or just Glasgow based but that really helped me a lot. Perhaps that's something to consider. The sessions are very daunting to begin with bt after a few weeks I actually realised that things aren't always as bad as what you make them out to be. If you don't have RAMH then ask your GP for advice or their local counselors - they should have a list
Hope that helps a little