Should I end a Friendship because I like her when she has a bf?

you don't really have to end your friendship. sure, she has a boyfriend, and it hurts like hell, but you're her best friend, you have to be there for her. you said it yourself, you don't want to lose your best friend. just be there for her and i doubt that she doesn't need you. every one needs his or her best friend even if it seems otherwise. :) hope this makes sense :)