I'm so pathetic and depressed because I didn't know Bitcoin quickly. What should I do? 
There is no such a wrong time to buy bitcoin, if you haven’t bought when it was cheaper than this, you can still buy now because it is still cheap to buy now if you compare it with what the worth of the price will be in several years to come. It will be nice if you buy now, there are lower units of bitcoin called Satoshi’s that you can still afford. Don’t still miss out of not buying at the price it is now, so that you don’t regret later of not buying at a lower price still.
Definitely there is no perfect time to buy the Bitcoins. We know how valuable Bitcoins are, hence whenever possible if you have extra funds, then just buy the Bitcoins irrespective of it’s price. Buy the Bitcoins and hold it for 3-4 years, you will definitely see 2x the profits. We have seen Bitcoins rising from completely nothing to 70k usd worth asset. So just stop complaining about the price and buy as much as you can.