Do I choose my best friend or boyfriend?

My boyfriend and I had a fight once. He told me not tell anyone about the subject of our fight as it was very personal and could cause people to judge if it spread. I understood and agreed.
I kept it in for months but eventually I told my best friend (for 10 years) about it.(My best friend (she) is also his friend) . I didn't realize they were also close as she mentioned it to him when they chatted after I told her.

Now my boyfriend is really mad and I'm not talking to my best friend coz I'm mad at her. Other people now know of our secret. My boyfriend thinks I'm the culprit for telling someone and is not mad at my best friend at all. He thinks I should not be mad at her and apologize for not talking to her.

My question is should I let them be close and back out ( end best friend relationship) or tell my boyfriend to backoff after I apologize?
Will being close to my best friend "work" if she's also close with him?
Do I choose my best friend or boyfriend?
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