The saying is old is gold. But As you will proceed in your life, sometimes you will have to start from zero. You will need to make new friends, new lifestyle. And the quicker you adapt to new things, the easier life will get. If you keep missing your old things, you won’t be able to enjoy the new beautiful things in your life.
I am not saying to eradicate old memories. Keep them but don’t allow them to take charge of your emotions. It is all about survival of the fittest, in order to survive you should always change yourself according to change in environment.