Many will tell otherwise, but I think it is fine to not have these friends, contacts and acquaintances etc. In my case I did put in effort to stay in touch, call up people after many years. But in most cases result was like "Okay, we were in same school/office/rpoject/neighborhood / waited for same bus etc...etc.. now what do you want from me?"

It maybe that you most definitely want it. However for me "missing out" hasn't make life any worse.