I'd recommend you talk to someone professional, especially since there is a history of substance abuse or something like that.
I'm also going to be straight with you, as I would want someone to be if I were in your place at your age.
What you learn from this may help you for the rest of your life, and I wish it does.
Your ex has many, many problems. It's not clear to me she's been officially diagnosed with BPD, but I'm going to assume she has the disorder or something in the same cluster of personality disorders.
She is someone who clearly is lacking in impulse control. She's grafting onto whoever is in her life at any given moment she thinks gives her what she needs or wants. Her needs could be emotional or physical at the time, but they echo each other. When she gets a temporary need or want satisfied, she either has a new need or want or the people she is with are no longer interested in her.
That's when she turns to you. You are a safe harbor for her. When she reaches out to you, she's trying to get a need or want satisfied. She might need attention. She might need affirmation. She might need to feel wanted. Whatever it is, that's why she reaches out to you. When you respond in one form or another, it satisfies that need, and she's no longer interested. That's why she goes silent and bounces over to another guy or whatever.
For you to have strength, you need to see her for what she is: a manipulator. She may or may not be conscious of her actions and motivations, but that doesn't matter. They result in the same thing, which is she has a itch, you scratch it, and then she's gone on to someone else. Every time she reaches out to you, you need to understand it's less you and more what you represent she's wanting.
That doesn't mean she might not have feelings for you. I'm not trying to be cold about this nor to discount that possibility. What I'm saying is her constant pattern of communicating and then going silent shows she's relying on you solely to soothe some issue she has at the moment.
I wouldn't want to be treated that way, and I broke it off with mine and went no contact because of it. It can hurt because if you have feelings for her, you're going to naturally want her to be in your life. But her actions are selfish, and her needs and wants will be never ending. And they are not reciprocal. She is not thinking of your needs and wants. She is only thinking of hers.
That means you have to think of your needs and wants. You have to not sublimate those to help her. You have to help yourself. Start by talking about it with a therapist. Chances are, they'll tell you to go no contact with her, as that may be best for both of you.
I appreciate it. She ended up messaging me again and saying she does miss me and wants to reconnect but she doesn't want me to see her like she is. She said she changed for the worse and that I deserve to be with someone who isn't a drug addict and
PLEASE READed in the head. I guess at least she was honest. I'm probably just gonna try and be strong and move on if thats how she feels. Part of me feels like she is just trying to let me down softly but I really don't know anymore. Don't really have it in me

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