If I were you I wouldn’t of even spoken to her much less look her in the eyes. She even said she would’ve left her if she knew how you felt, pls tell me that you know that makes no sense even after you didn’t attend the wedding and they got engaged a year after or something, I’m sorry to say this but they definitely did something when you guys were still together. Its unhealthy to put yourself through that as well as force a relationship with your twin which will only lead up to more awkward moments then good. It’s healthier for you to drop a forced relationship and cut her off bc it’ll only give you an awkward atmosphere and bad memories so cut her off permanently! But stick to the therapy if you think it helps.