Unfortunately, depression is part of diabetes, but just know that you are not alone here. All of us have felt sad, angry, depressed, et cetera, purely because of our diabetes. Talk to your doctor if you are really having a hard time, as it may be out of your control and time for medical advice.
Getting out there and sitting in the sun (like PaulaO suggested), watching your favorite movie, or just venting your feelings here are all great steps in feeling better.