How to get over old things?

Ive always had issues with mental health, and I take medicine for it. I get really upset and sick, but I never show it to my friends. It’s just not like me. I just don’t want them seeing me as weak or differently. Not my point. For awhile I’ve been basically haunted by this girl. We’re not friends anymore, used to be, and she keeps telling all of my friends stuff about me. And I feel like my friends are distancing. And I know I keep talking about this but I have no body to talk to this about and there’s not a day I don’t go thinking about this. I never told any of my other friends anything bad about the friend I’m not friends with because I think it’s so wrong. Part of me misses being her friend and seeing all the old photos of us, and I know I’m always going to a little no matter what, but then she goes talking about me to everyone. And the day we stopped being friends plays over and over. I’m so embarrassed about it. She pulled me aside at school and she sat there and acted so bratty to my face, and it hurt so much. it’s so sad thinking that was someone I used to speak to all the time. During that time I was in a really dark spot, and I cried at school. We walked to study hall, me just bawling while she enjoyed it. I feel so embarrassed being the one to break down and cry when I never do infront of my friends and that moment keeps replaying. She didn’t care how her words came off. She knows I struggle really bad and she knows I’ve been places because of it, but she keeps spreading stuff about me and I can’t get away. I never talk about her negativity, but that’s all I receive. I try to be so kind to all my friends. I buy them gifts and offer them everything, but I feel like no one will do it for me anymore. I want to move on so bad. I want to stop hurting myself and I really want friends. I just want to know how people do it. Sorry for talking about this so much, I just don’t know who to go to anymore.