Since when were miley cyrus and demi lovato BBF?

i was watching the lastest E! news last night, and one of the clips were of miley cyrus and her new scandalous photo shoot, and during the shoot miley was talking about how her BFF's demi and nick jonas dont use each other cuz they have their own thing going on, but still wat happened to demi and her BBF selena? and miley and her BFF mandy??