My friends are fighting over me?

Im 13 years old and have 2 GOOD friends. I have known one of them (Jess) for a very long time (scince i was 5) The other friend Lilly i have met when i joined hih school last year. Lilly was in my english cl and last year she burst into tears i was like OMG whats wrong she said she fell out with her group of friends. So i offered if she wanted to eat her lunch and hang round with m group of friends inbetween periods. Now Lilly and Jess HATE THE GUTS OF EACHOTHER!! I was best friends with lilly and Jess hated it she has always hated who i was mates with. It does my head in i mean i dont care if they dont get on but they bring me into it and make me choose between the two if them. Now because of this i hve removed my self from the situation and joined another group of friends and Lilly has followed me !!!!!! so now she has brought the problem over to this other group i moved to to get AWAY frow the issue and LILLY AND JESS!! now Jess thinks ive gone back to her whn i havent its getting so pathetic that Jess doesnt even like me walking from lesson to lesson with Lilly. I am in loads of lessons with Lilly and NONE with Jess! Lilly hates me being around Jess she is like ohh she is taking you off me she is trying to split us up! (wich she is right) Im sick of it. ive moved away frim the group and she followed me so what the HELL should i do!!!!!!!!!!! thank you if you had te pacients to read this lol xx