Friendship question. need help, advice. please!?

So I got this friend who I have had for 17 1/2 years. Im 19. We have been best friend for like ever. We bearly see eachother anymore, but were always here for eachother. And I got this other friend, who I work with and I have been friends with four two years. And me her, and three other friends hang out all the time, and party together, and know almost everything about eachother. And at once these two friends of mine were friends. And my friend that I have been friends with for 17 years was talking to this guy for like 10 monthd, then they finally started dating, and she lost his virginity to him, and they were together for a few months, and so on.. and after they broke up, she was still not over him and still wants him, and you know the rest..' story of the lost obsessed! Girl'. And now this other girl that I'm friends with, started talking to this kid, and they have prolly been talking for about 5 months. And they had and yeah yeah... but my other friend still ***** him too, and me not knowing about any of this.. I find out and have to tell eachother what's going on, and now the friend I work with wanted to beat my best friend up, but it never happend, long story, and one the reasons why she won't beat my best friend up, is because she has respect for me. But. Few months go by, and this happenes again. And yet again I'm in the middle of it. My best friend is still ******* with him, and my friend I work with.. kinda sorta does. But nowmy best friend is sorta mad at me, because I won't do anything about the situation, and I ask her what she wants me to do, and she's like nothing, and I'm like well then I don't get what you mean.. and she's like forget it. (Like being mad) and imlike ok??. And she won't say anything back. So if anybody knows what to do.. advice would be great. Please help!