My best friend that I've known for 5 years stopped talking to me. What do I do?

Its probably the fact before she started hanging with this girl alot and know one else,so she got really closer to here,bc they had something in common so they clicked,and she probably started forgetting all her other friends. and when her and this guy broke up she has been already hanging with this girl,and when that happen its not one of those things you just go running back to your life you kind of just go with the flow and go with how her life has been hanging with this girl,you just might have to pull her back into her old life again and back to where things were before this guy,which might be hard if she likes how things are already going,so best of luck