Girls, how do I convince my girlfriend and female best friend not to hate each other?

Here's something that has been going on since past few months. I used to date a girl which my female bestfriend did not like at all, but after 1.5 years of dating we broke up due to some reasons (no cheating no heartbreaking). But recently after 4 years, we met few months ago and things went other way and we somehow started dating again. And it's much better than what it was (it's not a toxic relationship). But here's the problem, i know my female bestfriend likes me somewhere but she never tells me as she is already dating. Actions do speak and i always notice it. But now, my bestfriend and my girlfriend are the greatest enemy of each other. Sometimes my bestfriend even says things to me like "Don't mention her name I'll fuck her up someday". And its quite the same from my girlfriend as well. How do I solve this and come to a mutual understanding as one has been my bestfriend since past 8 years and other one i first started dating her 7 years ago. They both are important in my life.

Girls, how do I convince my girlfriend and female best friend not to hate each other?
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