Husband’s brother has left his parter of 5 years and got together with the OW (they’ve been on and off for three years) I’m not a fan of her as the first time I met her (and last time they had ‘separated’ as he’d gone back to original gf) she caused some issues in our very early relationship. She seemed to try to exclude me from the group, kept trying to drape herself over my partner and drag him off to dance. I really have no desire to spend time with her but it feels like she and brother are going to want get together a and to play happy families (husbands family are extremely close and the ideal for the brothers would be for us to become a bit of a foursome) how do I keep boundaries to protect my mental health but also keep the peace?