Friendship strain

I have been best(?) friends with my friend Valerie since 5th grade. We are in 11th grade now and she is emotionally a draining person to be around. I never have any fun and she is rude and stresses me out. She is also a pathological liar and won't admit to it. However I love her family and she has been going through a rough time this year. I have talked to her about it many times and it's been about 2 years i have felt this way. I want to cut ties but will it make me a bad person? Any advice?