Can’t bring myself to leave my abusive relationship... please help

I’m getting to the point where I’m ready to leave my abusive relationship, but I just can’t leave. This is extremely long but I am in desperate need of guidance. if anyone has gone through this or just has an outside perspective I would so greatly appreciate it. My boyfriend is 41 and I’m 26. We’ve been together for 5 years. He has severe borderline personality disorder. So to put it very simply, in his case he will have episodes of extreme rage over things that would be minor annoyances to others, and since I’m with him I’m usually the target of these episodes. For example, today he felt that I was taking too long wiping down the groceries I just bought, so he came in the kitchen and kicked them all over the floor. Then he came back in and kicked them multiple times again. Things like that happen often. I truly do love him so much. Despite his issues he is a really good person at heart. He has been there for me through the good and the bad and helped me out many times. At the end of the day he’s always been there. When he’s not upset he is loving and caring to me. The abuse has been verbal since we started dating and eventually started with throwing objects and stuff. I am at fault for some of it, I am messy and lazy sometimes, and my anxiety and depression in this relationship have made that worse. I am far from perfect. A lot of times I feel like I deserve the way he treats me. His behavior HAS gotten better since the first couple years but he still has his episodes. An old friend who knows my situation contacted me about a month ago, gave me a gentle wake up call that I’ve gotten comfortable abused, and is offering to help me get out. Everything has fallen into place that I finally have an opportunity to safely leave but I’m having a hard time biting up the nerve, for a couple reasons that I can recognize 1. Mental health. When I was 20 and we started dating, I had gone through some traumatic experiences and wasn’t doing great emotionally. As fucked up as it is, even with the abuse the relationship provided the stability I needed to get my head on straight. I had someone who cared about me, a home to come back to every night, structure, and his family as well. I am terrified that if I lose the life I’ve gotten used to, and the stability, that I’m going to spiral out and lose myself. I don’t really have a support system. I know that’s selfish. I am planning on starting therapy but I’m still very worried about this 2. Missing him. Despite the bad times, he has been my best friend for the last 5 years. We’ve spent all our time together, and everything reminds me of him. He’s always on my mind, we talk all day long. I can’t even imagine going to the store and not picking up a soda for him, as stupid as it sounds, the thought breaks my heart. Just not having the biggest part of my life in my life anymore. My life has been stable and exactly the same for five years. I’m scared for everything to change and to feel lost again. 3. Guilt. I know he would be really hurt and lonely if I left him. He’s very sensitive. By now I’ve learned that he just truly doesn’t/can’t understand that his behavior is wrong and me leaving won’t change that. It’s my fault for setting the precedent that I will tolerate his abusive behavior. It’s going to hurt him and he’s not going to understand why I’m leaving. I take care of so much for him, and I’m afraid of how he will cope by himself. Like I’m afraid he will stop taking his medications. He has been suicidal in the past and says things like he’s just waiting for me to leave so he can kill himself. I don’t ever want to contribute to making him feel that way and I couldn’t live with myself if he hurt himself. 4. Leaving my dog. My baby is 2 years old and the sweetest, most loving dog I’ve ever met. We raised him together but he is legally my boyfriends dog. When my boyfriend yells at me he will crawl on top of me and lick my tears away. We love each other so much and he doesn’t know life without me. I really feel that he’s a blessing, he has been the light of my life through the darkness of my relationship. Aside from legal reasons and the fact that my boyfriend would come after me, I know in my heart it would be cruel for me to separate them because they’re together 24/7 because he doesn’t work, and they are bonded as well. It’s the idea of my puppy missing me, and not knowing why I left one day and never came back absolutely destroys me. This part is hard for me to even think about. Is the right thing to do stay for my dog? I just feel crazy and so sad. I know in my head I have to leave, but it just feels SO WRONG. Everything in me is telling me I’m making the wrong decision and that I need to stay. I feel like I’m abandoning my family. It seems like whatever I do, I’m doing the wrong thing. Now the friend that is offering to help me is getting frustrated that I’m taking so long, doesn’t understand why it’s so hard for me to leave, which I understand. I’m sorry this is so long, there’s very few people in my life I can talk to about this. The opportunity I have to leave won’t last forever. Please help!