why i can't be strong like other people??

It is true I am easily hurt. I like her and I trust her. But sometime I find that if someone avoids me, that HURTS me most. I dont know the reason for that. Today such thing happend and I was devasted. After such thing happens to me, I become childish and then again after few days I am normal. Is it some sort of insecurity? Why I feel vunrable? Why I can't be strong like other people? I don't know why???