I can't seem to let anybody get close to me

I haven't really payed attention to it before, but every time I've had heartbreak in my past relationships I've gotten mentally stronger. i don't fear death anymore, I'm a black belt in martial arts, I practice kendo. I'm a lot stronger, but at what cost? I'm seeing this one girl and I realize that I'm constantly pushing her away. Not just her, but I keep my friends at arm length. it's like I built a castle around myself. I don't feel like I need anybody but myself anymore. Is this normal behavior?

It is when your pain is trying to make you trip over your problems. The root cause needs to be dealt with. This program here is some serious, nuclear powered self help. If you're disciplined enough for martial art then you can do this: http://www.barbaradeangelis.com/cart/itemlist.asp?catcode=35

Ya its normal. Just protecting yourself from getting hurt bruh ;D You will find someone that will bring your little walls down. Just be sure that the one who does wont fck you up and cause you to raise some bigger ones.

Well it would be more so a question as to why you feel this way. Suddenly pushing people away is normal at time but has more so to do with the reasoning behind it. Some push people away because they feel they are headed down a destructive path and don't want those the care about to get hurt. Whereas other do it to prevent themselves from being hurt by those they have grown attached too. As far as I can tell you are on a path of self improvement, this is good for you because you are becoming stronger both physical and apparently mentally. My guess is you have push yourself toward self improvement so much that you than you might feel as though if you get close you will somehow become weak again. You might have also developed Narcissistic tendencies. But I am no Psychologist so I could be completely wrong.

Thanks for the comments. I started martial arts just like you said Jean, to not feel weak anymore. But now it feels like an obsession. I managed to get rid of the feeling that life wasn't worth living, but I think I lost some of my humanity too.

Lol you let a few women bring you that low ;D You're better than that

Totally understandable. I actually do the same thing. I mean, I'm friendly and everything, but once things get... Serious... I pull back. Way back. Like square one, sometimes. But I also try to not let go all the way. I'm just complicated that way.

It has a name and it's called intimacy issues aka the reason most relationships fail. It can happen at different periods of life and is often linked to a trauma that can sometimes go back waaay into childhood such as an absent parent and or a divorce to more extreme cases like rape, sexual abuse and whatnot. Basically fear of intimacy isn't only physical/sexual but also emotional, and it can be extended to romantic partners as well as friends and family. http://en.wikipedia.org/wiki/Fear_of_intimacy

Yep. Definitely childhood issues here. XD my childhood was a mess. Basically, it showed me nobody wants me unconditionally. You have to be somebody else for people to like you. But also, if you can't be yourself, then what's the point?