Biting skin inside of mouth

I have been biting the skin inside of my mouth for years, right after I stopped my habit of biting my fingernails and lips. I start from using my teeth to pull at the skin until it tears, then slowly working around the 'open' space until the whole area is 'skinless' so to speak. It'd make my face all contorted trying to reach certain parts of the skin (lol) Then I realised it is easier to use a piece of tissue or the front of the shirt to reach in, pinch and pull out the skin through my fingernails. So I would end up with bloody shirts and a sore mouth. The skin grows pretty quickly within 1-2 days, and the pattern would start again. Sometimes the wound would be so deep that a small thicker patch of skin would grow over the next day and I take pleasure in scraping it out each day, leaving the wound open again and again. I am not sure if this is the true cause, but I noticed there is skin discoloration at the two side below my mouth: the exact two sides where I bite on the inside. The skin looks darker there and people often think I bruised myself. I tried lightening the areas with make up but it doesn't really seem to work. Do other skin biters experience this? Or is it due to other causes? Or if it's permanent? I really want to stop the habit. But sometimes I feel the feeling of satisfaction I get is almost too good to give up. =\