Dear gameraddict,
First, don't blame yourself for it will do nothing but send you into a spiral of depression.
Second, learn some self control. Start with small promises to yourself, keep and repeat the promises. You have to do it everyday, at the same time; rain or shine.
Three, you're working for yourself so you set the time when you work and when you play. When you have a plan, apply second.
Four, there are many types of people. Some people are better in the office. Some are better when they work at home. It is obvious that you do not work well when you are at home, so GET OUT. Go to coffee shop or join a co-working space.
Five, punish yourself. Since you answer to no one (except for maybe your clients), you need to be able to punish yourself. For every promise that you couldn't keep, you can't play for the entire day.
I was in a similar position as you are. Although I didn't quit my job, but I do have a lot of side projects. At the time, when I was working all I could think about are the games and what sorta of things I could be doing (i also play diablo). I would deliver the projects late and would always have some stupid excuse about it. In time, I was very bitter, dishonest, and not very happy with myself. I did some research and read up on game addiction or other bad habits and put together the list above for myself. It was really hard the first 2 or 3 weeks, it was even harder compared to when I quit smoking.
Over time, I am able to be very strict with the use my time. Now my fiance is complaining that Im too mechanic about it.
Hope you are able to overcome this. Good luck