HI and welcome to the forum. Many great people here with lots of wisdom, advice and support. Im sorry for what brought you here but please know all of us can probably say we have done things we wished we didnt, change some of our decisions from the past and taken care of things much quicker than we did. The thing is, that is in your past and you cannot change it and looking back and beating yourself up certainly will not help you. I agree with everyone that looking at it from a learning perspective and trying to figure out why you went back, stayed as long as you did etc would be a helpful way of making sure you do not do these same things again.
The book by Melanie Beattie is very helpful. I saw myself in there through the entire book. There are some stickies at the top of the forum that are also full of tips for you.
I applaud your strength to stay where you are and move on. Whether a person is an addict or not, we still love them. I hope you can find whatever it is you wish to do and continue on and make sure to take good care of YOU. It is a very hard lesson learned. Hugs.