when I was young our dad left us, and we suffered a lot after this experience, I remember that I missed him a lot, but this suffering made a change in myside, now I don't miss really people or friends. I can miss just a small degree, not as I was in the past.

Missing someone is the best sad feeling 

Don't get used to anything, and you'll never lack anything.

Completely disagree.I move around a lot in my life,and so I am always missing friends and family in other places.But I love travelling so I am prepared to suffer missing people.We cannot stay in the same place and not connect to people and become friends with them.The alternative is never to make any friends.I don't accept that alternative.