My friend chose her best friend’s ex over her best friend

One of my friends, A, chose her best friend’s ex over her best friend. And I don’t know what to do about it. My friend, L, dated a guy (K) who turned out to be abusive and after 5 months, they broke up. Everything was fine until A came to me saying that she still liked K. She had a crush on K for 3 years. L came to school and told me she liked K too, and A said it was fine and she didn’t like K no more. L dated K, and then they broke up. After A told everyone, she then told L that she still liked K. L told A that it was fine to go after K, and after a few months, K and A began to talk. A and L are very close, having gone through the same experiences which brought them together. They both talk to each other about everything. A knows what K did to L, and all the abusive things K does because L talks to her about it. But when K and A talk to each other, A barely says anything to L about what’s happening between A and K. After a week, A came to L and told her that she was uncomfortable with L talking about her ex to A when she was talking to him, and wanted her to stop. It was a situation between the both of them, but me and some of my friends find out because L came to us about it. A tells L that their situation is different because they’re different people, and that K will treat A differently because she’s not L. But K is already doing the same things that he would do to L which already showed that it would be the same thing. Another thing is that they’ve only been talking for a week, so A doesn’t know much about K either way. A talks to L about her feelings and doesn’t consider what L feels about it. And L tells A the truth that she felt uncomfortable too but did it either way to make her best friend happy. Though sometimes, A would completely ignore L and not respond to her. Eventually, she made A choose between her or K. And…she chose K. I know they’re both in the wrong. L letting A be with her ex, and A choosing her ex over her best friend. But I don’t know what to even do. I don’t want to lose my friendship with A, and I know that they both didn’t want to lose their friendship. But I also can’t get the fact about A choosing L’s ex over her best friend. I just need help with what to do about this.