Should i try to get past it or move on?

I have been friends with Mary* over half my life, i became friends with Kate* 5 years ago. It was never a really easy friendship, she can be a user and tells a lot of lies. We recently fell out in a pretty bad way & i have no intention of fixing the 'friendship', i feel quite content to not be friends any longer. However Mary* who was there at the time of the fallin out didn't really support me at all, it really annoyed me as any time she has had anything going on in her life i am always there to support her. It has been some weeks now & i have spoked lightly to Mary* but i still feel quite angry towards her. She is complaining about feeling stuck between both Kate* & myself, i have not asked her to make a choice at all nor would i expect her to. I do feel though that we have been friends for so long that she should have at least supported me. I feel let down and i am unsure of whether to carry on the friendship. I'm beginning to think its not a rea friendship after all. Anyone have an advice for me?