Boyfriend Or Best friend?

So, heres the daily scope. I have an amazing best friend that we will call "E", and a loving boyfriend that we will call "P". Something not so loving/amazing, THEY CANT STAND EACHOTHER. Crazy right? You would think, they would get along for you. Wrong. In times I have to decide if its gonna be her day, or his day. I can barely even get them to talk, without pulling an ear or either making a scene. I have to give some credit to him though, because he did try to get it to work. E of course, being her total stubborn-self said screw off. Just my luck! Your prob. wondering what the heck is her deal, what does she have against him thats so bad? Well here's where it started.. Last year, E and I had an other best friend named K, she was dating P at the time. (Another dirty story, for another time) E and P got pretty tight, even flirted a little you could say. Until Miss K found out, it basically ruined E's and K's relationship pretty badly. E never got over it, and blames my boyfriend. Which sure, I would be pretty pissed too.. but it was a whole entire YEAR ago. Plus she can't just blame him, she texted and talked to him too. There's no need for grudges! Its hurting our friendship worse and worse. I can barely even bring up his name, or she starts getting standoffish. I've been thinking though.. is this all because of K? Or is she jealous? I talked it over with another friend, and she said maybe.. when her and P were talking when he was dating K she started to crush on him. I wish E would come out and tell me the truth if she did! But lifes not that easy. I hope this is finally blow over for good soon. I dont know how much longer i can handle it, before I have to chose who is gonna stay in my life, and who isnt. -W.