Why is everything changed?

I was thinking a lot either to post this here or not, and after a while, I saw that people here really help, and it;s a nice community.. so well... uh.. I just dont know what to do anymore...

well, I have a girlfriend, and we are together for 10...

month... the first two month were just incredible... we were the happiest together... and fell in love in first look...
but then after I just said smth wrong, and we had a fight... it ended up really fast... she forgave me, and we made up that very same day after a few hours...
but then again, after that everything began going so wrong...
we began fighting and arguing so much... she keeps saying that I've changed... and that im not like the one she fell inlove with... that I became more barbarian, less shy and nice like I was, less caring, less seeing and noticing her feelings, and it's true, I mean once I could look in her eyes and tell exactly what she feels and wants... but now it;s not like this anymore... and it kills me, because I dont know what changed... why I changed... I just caused her so much pain...
can someone please tell me whats wrong? why I changed? what changed? how do I change back? how do I stop making her hate me? how do I make her love me? I dont want us to end... this cant be the end.. although what she says after I get her mad, I still love her so much, and want to be with her for as long as life lasts, and after... but I dont want to hurt her... why is it so much to ask to be happy with the one I love? why do I ruin every relation ship I have? please help me guys

well im a girl and I think the prob is you both grew out of eachother you mite think you love each other but you dont you change because your growing and you fell diff ways bout thing and same wiff her it wont last any long you both grew out of each other so you should end it now befor you guys hate each other but stay friends and if you get the same felling you got when you 1st sall her then that means take another shot at i5t with her you both just need to get your feelings strat

oh... I understand... thank you...

just one last question, why is that happening? how can such insane love actually end?...
we just saw each other, and we had butterflies in our stomachs...
and after two month, it just passed?... how can it be?