In all honesty you haven't CONVINCED yourself of anything or you wouldn't be having doubts about calling off the relationship. You feel like crap because you're unsure of the decision you've made. Why did you guys break up? Is it really worth throwing away a relationship you've got so much invested in? I'm sure you've asked yourself these questions and if calling off the relationship really is the right thing for you then first you have to stop beating yourself up about it. Then you have to move forward as hard as that may sound. Moving forward may consist of anything from reading a few self help books to maybe improve your next relationship. (you just might learn something about youself) Or it may simply involve taking some alone time for the very same reasons. All in all you will recover no matter what you choose. If you are second guessing your desicion it's time to do some serious soul searching.