I'm in trouble

by Lola
(Kunming, China)

Hi everyone. my name is lola and i'm 19 years old. I used to hang out with a group of girls. Well, we used to think we were tight,and caring about each others problems, insecurities, well, we used to think we were BFFs.
Unfortunately, turns out, one of my 'friends' was sleeping with the boyfriend of another girl in the group. He told me, turns out it was true. I wanted to tell my other friend, but I got scared about how she would react. Turns out now she knows but more importantly she knows that I was aware of the whole story. She's mad at me, and I feel guilty.
What should I do, please help me.
Thank you in advance,