Husbands identical twin is dating and in “love”w/my husbands ex; she tried to get with my husband, after he told her we were together. What do I do?

Backstory- I started dating my husband 12 years ago, he went to a party and this girl who he claims was “just sex” tried to get with him- after he told her we were together. She then was very emotional and cried-seemed devastated. Now she is dating his identical twin, and they are “in love” My husbands family think I should just forgive and be okay with this because my BIL has been single for along time. I truley care about my brother in law, this situation literally makes me sick, the thought of having have holidays, just makes me sick. What should I do?
Husbands identical twin is dating and in “love”w/my husbands ex; she tried to get with my husband, after he told her we were together. What do I do?
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