Congrats, seriously.
It was drinking that cost me... After doing just about every drug known to man, the only two I had a hard time putting down were the two legal ones, go fucking figure. People that loved me tried to get me to go to rehab, but I fought them. It wasn't until I lost everything in the span of six weeks or so (job, wife, girlfriend, good friends, house, cat, dog, and nearly my freedom and life) that I decided to go on my own. I damn near killed myself over it all, it got so bad. If some epoxy had set properly on the death mask I was building, I wouldn't be here to write this.
After all of that, I checked myself in to an outpatient deal. Hell, even then, going was more of a cynical ploy to make myself look better when I went to court. At that point I was sober on my own, so why bother going, ya know? After a few days of it, that started to change, and it became something I really wanted. I actually looked forward to getting up and going a few days a week.
Here's a few things I can tell you based on my experiences and those of the people I met, and I hope you take them to heart:
You will get out of it what you put in. Dedicate yourself to it if you really want to see a change.
Do yourself a favor, get a notebook. Write every day.
Forgive yourself, but don't forget. You can't change the past, and beating yourself up won't do any good. At the same time, remembering how bad things got, and knowing that you could be right back there if you use again can be a powerful motivator.
Many addicts are the smartest people you will ever meet. Find others who are as dedicated to recovery as you want to be, and learn everything you can from them. These will likely be the ones who are there on their own. Many others will be there for someone else, and their odds aren't nearly as good. You'll see people who are practically begging for a relapse. Learn from them too.
Even if you feel like 12 step is not so great, that doesn't mean there isn't value. If nothing else, there can be a sense of solidarity with other people there. Speaker meetings are usually interesting. I personally prefer SMART Recovery (no god stuff, more science), but it doesn't matter what you do, just find what works for you and do it.
Boredom is going to be your biggest enemy. Plan for that.
Good luck!