Parents being unreasonable???

Ive known Arial sense i was a baby ever sense then weve been bffs. Today i started talking to my mom about skin i brought up Ariel and somehow we got to talking about Arial's sister Kelsey. Than i brought up how Kelsey's boyfriend is a jerk. My mom went into judgment christian freak mode and asked in a awful tone "DOES HE SLEEP OVER!" I did not want to lie to my mom. I made the mistake of answering honestly. I said "yea sometimes" She had an evil look on her face and said "YOU CANT GO TO ARIELS ANYMORE!" I told her that was unfair and walked inside my house. Minuets later Ariel called asking if i could come over I said "Only if your sisters boyfriend is not there" Ariel said "Oh they broke up!!" I said "YES!! and began to sing Halaluya!" Than i put down the phone and asked if i could go to Ariels & told her that Kelsey & her Bf broke up" She still said no. I dont understand why my mother is being this way can someone tell me how to handle this i love my bff more than anything HELP ME!!