Cleaning out the friendship closet

So, I have this friend who is a b***h. She's manipulative and controlling and always wants me to be down with her at whatever level she's operating on. I have been separating myself from her but I always feel guilty for either leaving her stranded or feeding into her negativity. Every piece of advice she gives me results in me hurting myself or dwelling in the negative. We've been friends since high school so I guess it's natural to grow apart. I just don't understand why anyone would try to hold down another person. So, I guess that leaves me in denial about it. I think this may all have to do with my self-esteem. This is a bad habit that I need to break. Why do I keep telling myself that I don't deserve better? If God already forgave me, what do I care what she has to say? She's not bigger than God.