I am in a relationship I dont want to be in, what should I do?

I have been with this guy for 2-3 months and I have tried to break it off multiple times but he starts begging to stay together and to give him another try and I end up changing my mind because I don't want to be a bad person. But spending time with him is not enjoyable for me at all and he has said a lot of problematic things to me before (such as I don't deserve him, all the guys I dated are unattractive etc).
He is also too much into sexting, something i have made clear i don't like and he acts like its my fault that he is losing interest in doing anything intimate with me. When i bring up that maybe we should break up then he tells me to stop threatening him.
I really need some advice in how to break this off because it is really messing with my mental health.
I am in a relationship I dont want to be in, what should I do?
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