Friendship/relationship clash

Hi! My partner has DID and his alter (H) is in love with our mutual friend (K). K has known H since they were children, and is in a relationship and has a baby with a man with anger issues (S) she had confided in me a lot about him and they had broken up. This was all fine and managed until H started to deteriorate as she gave him hot and cold treatment. The push and pull is literally pushing him closer to going dormant so I was going to talk to him the next day as K was giving him false hope by not telling him that after her and S broke up they got back together and we’re moving in together. This is important because K had stated after they’d broken up that her and baby were going to be free and gave the impression that they were completely done. Before I could talk to him about it I had given my partner my phone to plug in while I made food and he had started talking to K pretending to be me. telling her that she needs to distance herself almost completely and speaking about S in a way that I would never have done. The way we type is completely different and she didn’t notice and due to the way he worded it K thinks it was me and it has destroyed our friendship. I’m not in a position to tell her because 1 why would she believe me and 2 if she does then she loses 3 friends instead of 1 and I don’t want that for her. She is still messaging H completely fine but I don’t know if our friendship is reparable and what is strange is my partner is refusing to let her know we are in a relationship and when I tried to tell her he lied over it so from her point of view I’m just like everyone else and jealous and I don’t know if I can fix the damage that’s been done