Hi, I'd say that you really are being too hard on yourself. It has to be one day a a time, and one/two weeks off is GREAT, every single one of those days still count!! So give yourself REAL credit for those days and remind yourself that this does NOT mean you're back at square one. Hey, you've shown you have it in you to stay away for that long, that's something you have behind you!
Now just keep the focus as strong as it was before on managing another day.......and another day........slips might (or might not) come along the way but they don't have to define you if you can just try to get straight back in there.
And from each period you're clean just try to learn/take away something, anything, even a thought pattern that has helped you along the way in doing that. It may not help every time (IF you slip again) but just working on building up that armory has to be a good thing. So, no, you haven't just thrown away that time when you were clean, you've more made some great progress to follow up on. One day at a time, and there CAN be MANY more days.
Best wishes
Alison