My partner (27F) and I (26M) have been together for about a year. We live together. Throughout our relationship, my partner has been jealous of my friendship with my best friend (25F) of 4 years. This has been manifested by her sending me passive aggressive messages and saying hateful things about my best friend whenever I hang out with said friend (and usually other friends). This makes me feel very anxious and uncomfortable.
Because of that behaviour, I started seeing my friend less and not telling my partner the truth about what I was doing, out of fear of a reaction. This caused her to feel excluded from our friendship which seems to have intensified the jealousy. She also feels that my best friend made little effort with her. In my best friend's defense, she did invite both of us to a couple of her house parties, however during those parties she and my partner did not speak much. That being said, I suppose my friend could have done more. Recently my partner called me saying that she cannot handle it any more and wanted to break up. I felt like I was forced to choose between my best friend and my partner and I made an extremely emotionally difficult decision to break it off with my best friend to save our relationship. Since then, I felt lonely, depressed as well as been feeling like I made a terrible decision and constantly think about changing my mind.
How do I communicate to my partner that I cannot emotionally handle breaking it off with my best friend just because she doesn't like her?