Sometimes it is okay to stop being friends with someone.
Sure, it might be really hard to not be friends with someone that once used to mean everything to you. It might be hard at first to not have that person to text first when something happens in your life that you need to tell them about. But it eventually will get easier and you will eventually realize that your mental health is better now that a negative relationship in your life anymore.
Think about it, you wouldn't have even thought about not being friends with them anymore if that relationship was a positive one. If it was a positive one you would find a way to work through the issue that you are having and yes, every relationship and friendship has some form of an argument that makes things a little rocky. But if the relationship is positive you will fight for it.
At the end of the day if you are in a negative relationship or a toxic friendship it is okay to let go of the relationship and start focusing on you and the positive relationships and friendships in your life.
Letting go of toxic relationships will also help your mental health. You will feel better. You will no longer feel like you don't matter to that person.
You will start to care more about yourself and less about the toxic relationship. You will smile more. You will have times where you want to text that person or call them and tell them about something that happened in your life but you will eventually find another person that will take that spot in your life and they will be the positive person that you wish you would have known sooner and that you are grateful that you know now.