Why does pain have such a hold on us?

When we are babies we learn to cry when we are in pain, that way it can be alleviated some how, but as we get older it becomes uncommon to cry, atleast for guys it is. With my last serious girlfriend when I broke up with her she got very mad at me during it, not for the break up itself but for the fact that I didn't cry. She told me I wasn't showing any emotion what so ever, truth betold I was in a large amount of pain, not so much because of the break up since I understood I had to break up with her, but because my ideas of love and everything that went with it were so damage that their foundations began to crumble. A few weeks before I ended things with her it was valentines day, being the hopeless romantic I was back then I had plans for us, I was to pick her up at 10am and we were going out to dinner and shopping at the mall which she wanted to do. This was going to be on Saturday so during the week I left her notes hidden in places, I put roses in her car. I also bought a small hand crafted box with rose designs in the top, filled it with heart shaped red glitter deals and a pink rose candle. I left with the box a note telling her that all my love for her was in that box for her to keep. It occurs to me now that maybe I put all my love in that box and I should really ask for it back even though it is very unlikely that I would get it back, she would probably throw it at me now. So then sat. comes along and I get there at 10am to pick her up and she is mad at me, I don't know what about at first but soon I find out that I am late even though I was there at 10am and we said 10am. So we enter the car and start to head to the mall and I soon find myself to be the target of a full seemed at the time tatically planned assault. She puts me down in every way possible, calling me many different names, naming off all my bad qualities, comparing those qualities to her ex saying how much better he was then I am and how I am so pathetic I should be so thankful she would even consider being my girlfriend. I think thats the first time a girl has almost made me cry, well I actually had a tear run down the side of my face, I was so mad I turned the car around, took her back to her house and told her to get the hell out of my car. She didn't do this and we made up a little bit later, then two weeks later I broke up with her and I quote she said, "I never saw this coming, why are you doing this?" After that day I haven't cried a tear or even come close to one, I have carried the pain from that day with me ever since like chains that I drag on the ground that slow me down and never let me go. This same pain keeps me from forming anything with any other girl or ever trusting one, I lost my hopeless romantic side because of it and as much as I try I can't seem to find it again. This is what pain is to me, it changed me, stole a part of me and I carry the scars from it still to this day, also this is a silent pain because if you ever asked anyone they wouldn't be able to see it, they believe me to be happy and without trouble when it comes to girls or relationships but they couldn't be more wrong. So I ask you what is pain to you, do you know of pain like mine that seems neverending???