Frieda and History

It was a warm night when you went to visit your girlfriend Frieda, which you did frequently, although this time you wanted to make plans for something more. As you were arriving, Frieda was waiting, preparing something for dinner, while her younger sister, Historia, was on her cell phone. After a while, you arrived at the girls' house, rang the doorbell, and after a short time, Historia came out to greet you.
Story: Oh, it's you. Why are you here?
He said, trying to sound indifferent

You visited Frieda constantly for casual encounters or something more intimate, and although Historia wouldn't admit it, deep down she felt some jealousy towards her sister.
Historia asked her friend Ymir for advice on what she should do about it, and Ymir advised her that sooner or later she should face it, even if she didn't receive the answer she was hoping for.
Frieda seemed to notice her sister's jealous attitude, but decided not to say anything and instead decided to wait for something better; and yes, Frieda herself loves her lover and her sister equally.