I 21F love 23M, but am not happy anymore. How to break up?

I 21F have been with 23M for almost 3 years now. Our anniversary is actually a month away. For the first two years of our relationship we were madly in love. We only had few disagreements, we spent a lot of time together, we stuck through COVID, and were simply a happy couple. Then all of it changed. After our second anniversary things started to get more difficult between us. We were bumping heads a lot and we both said things that we regret. I believe this is when our relationship starting becoming very hot and cold. There would be times when everything was so lovely and amazing and then there were other periods of time when I would cry a lot because his character was off.

My boyfriend recently graduated college and was put under a lot of stress by his dad to find a job and start his career. Up to the point where his dad would get physical with him and verbally abusive. I tried being there for him, but he started having less and less time to communicate with me. He would seek comfort with me after his dad would do something, but sometime later he started resenting me more and more. He even blamed me for his dad hitting him and told me he hated me because of it. Which I thought was strange because his dad doesn’t even know me.

From then on his entire demeaner towards me changed. It was like I was dating a completely different person. This new him was mean and cold, but I stuck with him through all of it because there would be times when the old him would show up. Our relationship was very hot and cold, then hot and cold again. He would tell me he loved me, bought me gifts, helped give me college advice. And then he would tell me that he hated me, that I should die in an accident, that i’m annoying, and he made jokes about physically hurting me. These things scared me and caused me a lot of mental stress, but I kept getting reeled back in when he was nice and loving again.

I know this isn’t right, but I can’t stop waiting for him to come back. I know that he’s in there somewhere. How can someone change so drastically. I have all these memories and pictures, but now thinking back on them make me cry.

This is my first relationship. Part of me still loves him despite all the hurt we both have been through. I need to end the relationship, but I don’t know how to. I admit, i’m a little scared of how he will react. We don’t live in the same city, so i’m planning on calling him instead.

TLDR: Despite a seemingly amazing relationship for the first two years. The start of year 3 has been mental anguish with me 21F struggling with a hot and cold relationship with 23M. I know that I need to break up, but need advice on how to handle his reaction via phone call.