Stop buying bitcoin is depend on you mate. If you don't have any belief in it, you must stop buying. But if you believed that bitcoin has a better future better for you hold in a long term, just simple as that.
It is not about the belief that you have for bitcoin because it is all about the price and the movement of the price in the market, if you see that the market's price is not in a good shape and more like it will dump then you should stop buying and you need to think if you want to sell so you can be able to secure your money.