There are good days, and there are bad days. This is a completely natural reaction to a breakup, after all. I haven't a clue what the circumstances are surrounding your breakup, but I can tell you that even in the worst sort of scenario people will second-guess themselves over and over. The best thing you can do is know what you're feeling, let yourself feel it, and then let yourself heal. Time is the best way of going about this, of course.
You will have bumps along the way, but you will get to where you feel better, even if the hollowness never completely goes away.

Hang in there, and remember you've always got Loveshack to come to when you're feeling low.
Best wishes!
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"Mom...The Easter Bunny...HAS EGGS!!" My four year old daughter as she literally falls to the ground laughing hysterically, marking one of the most completely absurd yet strangely fulfilling moments in my life - ever.