why can't i let go of my past

...I've been kicked, punch, spit, and cursed and i almost lost my life...because my bro entered a frat and he committed violations to an opponent frat. Since he is all the time around his bros, he can't be touched and being revenged to. I, being secretly identified to be his sibling...i paid the cost...i have harbored those ill feelings deep inside me ----alone....alone...yes. I slowly moved on and lived a happy life after that, thought it was....later, after 30 years, of loving and living and leaving, i met a new young cute guy.... I secretly browsed his FB and knew that most of his friends are member of that frat. After 2 years, I have now the courage to ask him if indeed he is one of 'em. And the simple "yes" dumbfounded me...Whaat???? I shouted, pak! Pak! I have not controlled myself, my world became dark, I was trembling in anger and I was crying while I attacked him inside my car along a heavy trafficked area, I was out of control and the rest I don't know what I did. He just let me loose out my anger...