I have this real big hate on this person?

I cant take it anymore, i hate this person so much i get a stomach ache when thinking of the person, I even wished death upon him but of coarse i would never do that, i was just so angry and it felt better when i said to the person that i wished they were dead. The problem is i hate the person for reasons in the past and i though i ws done with them, then my best friend got friends with the person i hate, i was happy for my friend of coarse i mean he is my best friend and i am happy when he found a new friend. Then we talked and he started talking about the person i hate very much like every day, i never said something cause i mean he is my friend and he is happy talking with me about his new friend but it started getting annoying and i felt realy bad about it because my friend like the person but i hated the person. Then he started telling me things the person told him about me behind my back, he told me the person said that things me and that person did in the past were all crap and dumb ect. and it really hurt me cause that was the only good memory i had from the friendship i had with the person i now had, so i just exploded cause i couldnt take it anymore my best friend talking about this person all the time and that person talking behind my back, so thats when i said i wish you were dead to the person and that they were the worst person i have ever met in my life. Then my best friend stopped talking about that person and i once again though the topic was over again but he managed to after like 3 weeks bring the topic up again and now he starts again and i always sit there on the phone going ah ok yeah very nice when he talks with me about this person, but he doesnt get i dont wanna talk about it and every time he talks about the person it hurts me cause it reminds me of the time i didnt hate that person and the way the person made me feel bad for such a long time and it just hurts... anyways i wanted to take some time away from my best friend cause i know when i confront him with the thing that he should keep it down talking about the person, my best friend will tik-out and say yeah do this and that and i wanna talk about that person cause blablabla. But i cant just go away and not say why i wanna take a break cause i mean he is my best friend. :( i feels so full of hate and everything and it is starting to also go on my best friend cause he always brings this person up, i just wanna have a break and relax from that sad felling i get from him talking about that person. Pease Help!!!! Thank you in advance, i hope its ok that i didnt give names as i want to keep the names of the involved private :)