You may be experiencing some Seasonal affective disorder (SAD), also known as winter depression. Make sure you get plenty of sunlight in your home or get out and soak up the rays on a good day.
I understand how your feeling down after a relationship that did not grow. Let go of this one, put it behind you. Remind yourself you are a wonderful and caring person and stop the spiral. Just don't give in to the easy way out and start working back up out of the funk.
You have all of us to support you so hang on sweetie.