I regret leaving bitcoin; last time 1Bitcoin cost like $600 now look where it is now; i would've made a really good investment. I only had like 0.5Btc in my account; im glad it gained value but i know i could've earned so much more if i stayed.
But it's still better that you came back and started all over again than leaving it for good 
Rapidly fluctuation with the upgoing trend is bitcoin's nature so you can still gain lots of profit if you try hard. So no need to worry and regret, just keeping up with it as bitcoin will be fully developed and become main currency in the future.