Is it normal to realise the value of someone after they are no longer in your life?

I appreciate a lot of the good in people. I think everybody has good in them but everybody also has bad in them too. (Me included) Everybody I've dated has something that I liked about them or I wouldn't have dated them. Unfortunately, the bad usually outweighs the good. It seems that it usually takes a little while before the truth comes to the surface. In my experience, it seems that most people were out for themselves and what benefits to themselves. From my perspective, it seems that nobody really wants a permanent lifetime relationship. But yes to answer this question, there is something about everybody I loved that I miss.