It normal to feel this way... and think about the "what if's"
...what if you hadn't done certain things, hadn't broke up...things
would perhaps still be good... Also maybe it's a bit hard to
swallow sometimes, as we're all human, that her new bf could be
better, more suited to her than you... I'm not saying you're bad or
anything, it's just normal to make such comparison.
Nevertheless, when you meet a better gf, one who is more suited to
you and who loves you dearly and whom you love, you will see this
break-up as a blessing. 
