Why is my attachment deeper than most?

I am a very loyal guy, whether it's partners or friends. If I lose one of these, I am bound to have it on my mind a long time, and most of my friends will say "forget about them, their loss" and they prove that when they go through breakups or lose friends. I'm not sure why I've never been able to move on that quickly, the people I knew and lost feel so irreplaceable to me. Why is this?