Kimme - it's always a struggle, and we're not perfect people. That is what makes us, human.
As you know from your own experience, sometimes this process flows pretty easily; we're highly motivated, feeling good, looking forward in a positive way.... Then, life happens & knocks us off of our foundation. This by NO means makes you a failure. It makes you, human.
I've gotten a lot from your posts, and I feel confident that you will get back on track. Life is all about ebbs & flows, and I believe that a momentary setback will not stop you from moving forward on the path you charted for yourself.
And please please PLEASE stop beating yourself up and driving yourself crazy with the "I should'a done this, that or the other thing". That will only keep you in a negative state. Accept where you are.....and move forward. NOT easy, I know! You've come so far, and you can continue on.
A doctor once told me that success isn't being a perfect dieter. It's being someone who gets right back on track after blowing it. We all have to accept, that is the way it will always be. Life is not black & white. It's many shades of gray.