My boyfriend is asking me to go to his friend's apartment tomorrow. But the problem is I just hate her. I don't have any reason to hate her, she was always perfectly nice to me, but I just do. 

When I met her I was actually okay with her, but when I find out that she is in a relationship with an engaged man for a year and a half I just slip. She becomes all black to me. And now I can't stand her. I don't wanna talk about her, I don't wanna see her. Everything she does, it doesn't matter, in my mind, she is bad. 

He is aware that i don't like her but he wants me to go with him and if I don't he will go without me. And I am afraid that that will trigger me even more. 

I know that he can go there and later meet with me, but I also know that I would not want to see him after that. I want him to do whatever he wants, but I just don't know how to deal with this rage. And if he doesn't go I will just hate myself and feel like shit person. 

Can someone help me rationalize this?