Abusive relationship

So... I’ve been with the guy I’m currently with for 5 years. On our 5 year anniversary I left him for 3 days because he’s mentally and verbally abusive and I couldn’t take it anymore. During those 3 days, I had a guy I stopped talking to for my current boyfriend reach out to me. We reconnected as friends. We were best friends for years before I met my current. After 3 days, I got roped back in and I came home. My question is for people that have been in an abusive relationship before, how did you leave? Like how did you leave and stay gone, and get the strength and mindset to not hang onto someone you can’t change anymore. I love my current boyfriend so much that I cling to who he used to be before the abuse started. My mind is telling me i need to go, but for some reason my heart can’t let go completely. My mental health has been beat down so much in that past 3 years that I am scared to leave because I don’t know who I am as an individual, I’ve lived my life for this man for 5 years and I’m not sure who I am without him. But at the same time, I am unhappy and have voiced that to him, and he doesn’t nothing to fix it. I have a man waiting on me, waiting to give me the world and love me how I deserve to be loved, and I for some reason can’t let go of this POS I live with.