When i don't drink, I get depressed.?

I have been having 2 gles of wine a night for at least 20 years. Sometimes, I might have another one with dinner. I know I use alcohol as a stress reducer, and as a reward for getting thru the day. Problem is tho, I would like to stop this habit, and just drink socially. I find that when I try, I become depressed, and bitchy. I only have these two 5 oz gles of wine around 9pm, and never drink during the day; don't even think about it. Am I an alcoholic? Why does this mean so much to me, and how can I stop it? The thought of giving up drinking for good makes me depressed. They say if you have trouble giving it up, then you have a problem because you need it. Well, I need it. But is that bad? And how do I stop, and just drink socially, like one or two times a week with friends?