Who should I be more mad at?

my boyfriend dumped me a few months ago because he couldn't get along with my sister. After months of not knowing why we broke up he finally told me. My sister and my boyfriend had a hard time getting along with each other. They were cool one minute then drama would occur the next. When my boyfriend and her wouldn't be on good terms, she attempted to turn me against him. It never happened and I didn't blame him for anything. When things got worse between them, my boyfriend ghosted me including her. Later to let me know I did nothing wrong to cause it and that it was my sister fault. He had the option to not have anything to do with her but for whatever reason he felt the need to keep in contact with her.

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Who should I be more mad at?
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