Problem w/ a sister

[PM_Mama00]

Ok...so I have this problem with one of my sisters. She was going out with a guy from ABC Fraternity for 5 months, but they were very serious. Serious to the point where they were talking about marriage and all that, even though they were in their first year of college, and only 18. They had a bad breakup. But since he is a member of ABC, it's hard not to be friends with him. Plus he lives near me. He has come out to shoot pool with me and my firend a few times. Last nite she called me from his cell phone and yelled at me!! Saying that I didn't know about loyalty and all this other crap. And she added not to talk to her ever again. He has lied to her before about me, and I have a feeling he did again. I don't want to start anything with him cuz his brothers are awesome and I don't want problems with them (I have been there, done that). So what do all of you think I should do? Some say let her come to me, but with Rush coming up, it's gona be hard to be in a room with her for hours and have this tension!! Plus she is one of my sisters, and I love her dearly and I DO NOT want a guy to come between our friendship.