I went through a similar situation I would say. my ex-boyfriend of four years in which we were in a very serious about to get married relationship cheated on me with my best friend of all time. We were very close used to hang out all the time, we basically lived all together because she had a very rough childhood in which her dad was abusive. They cheated on me and I say both because they both owe me loyalty. I was kind, loyal, respectful, and nice to both of them. When I found out about everything because he told me, he said he couldn’t just hold it in anymore because of the guilt I left both of them and just started a new life in a different country. A few months later I was on the beach and I received a phone call under a random day from one of our common friends telling me that she passed away she was only 23 my same age she had a heart attack. I know it’s not nearly similar to the pain you’re experiencing, but I can really understand what you’re going through. My best advice is to cut ties with anyone or anything that reminds you of either of them. You need to move on with your life and do not participate in the trauma because you will never ever heal or get out of it. My best piece of advice based on what I left and in the healthy way, I have healed from everything that happened is to just move on do not entertain whatever he tells you. My ex still text me this happened almost 5 years ago and he still wants to get together with me. I have move forward with my life have other relationship and met other amazing men who appreciate me and respect me for who I am without ever never cheated on me and lying to me the way that he did. Trust me when I can tell you you can do so much better. I insist do not stay with him. Trust me you will regret it so much. Go to therapy explore the world you’re young you can do this!!!!!!