It is definitely discouraging to have a disease that is often unpredictable and has so many facets to manage! I get upset quite often at myself and at the disease, but I am still encouraged by talking about it both to family and to healthcare providers. Better management of diabetes even to add some constancy in removing hypo/hyper glycemic events does make a difference in your mood and in your sensitivity to blood glucose changes. Depression which is often an associated feature that goes hand in hand with our disease is treatable.
Let your team (personal, family, spouse, doctors) know how your are feeling in order to find a way to better manage it. I can't promise eliminating it or even making you feel better, but I think that having more good days than bad makes life bearable and more challenging.
I am less optimistic about a disease being found in our lifetime based on my contact with the researchers currently involved in the field, but I think that we are lucky enough to be living in the age where better tools to make our lives easier are arriving every year. I have felt pretty low in some periods of my life, but I often talk to my care team about it and have received some help, enough to say that I have more "good" days (from a mood and diabetes management perspective) than "bad" days and encourage others to seek help.
Nobody can help you unless you ask for help and take advantage of whatever care you might have at your disposal: nurses, spouse/significant other, therapist, community clinic, meet me group, etc.
You are not alone and life is worth living -- do not console yourself with thinking that you should not complain about it and that there must surely be others in worse situations that deal with life -- love yourself enough to ask for help. I care about you and this group cares about you, but as much as we may have good intentions, we do not wake up every morning thinking about the well-being of each member of this forum.
You took a first step and wrote about what you were feeling, not elaborate on that feeling by communicating it to people who have the power and willingness to help you design a plan to take action! I hear frustration, but also enough impetus in you to continue to fight this damn disease and not let it win -- manage it and realize that it is not completely under your control and will win sometimes -- you just have to make sure you win more often that it does.
I apologize for the long-winded stream of consciousness, but I have been where you are and have dug myself up and out -- I did it with help and it does not happen without some hard work and communication -- you can do it!