<human>: Can you give me the gist of the text in a nutshell?

Hi Reddit, im not here posting about my relationship. Knock on wood my relationship is pretty damn perfect. My friend however.... Heres a quick backstory. I know her for about 3 years now and we were coworkers when we both worked at Panera Bread. I know her now fiancé for 6 years through my brother, really chill dude, kinda goes with the flow. The two have been together for 8 years. They just lived apart for a long time.

  This morning she frantically messages me saying we need to meet up immediately. I panic because she didn't tell me why she was just hysterically crying, so off I go to her house which is 20 minutes by bus from mine. I get there and she still is crying but calm enough to talk. She tells me two nights ago and again last night she slept with her ex bf while her fiancé wasn't home. 

  At this point im absolutely floored, I don't know what to say, im still with her as I post this, shes just unaware what im doing. Ive been cheated on and I remember her fiancé telling me how fucked over he got by his high school sweetheart. Im so confused, I don't know what to even say to her to make her feel better. Shes a good friend of mine but so is he, not to bring time into this but ive been good friends with her fiancé way before she came into the picture. Hes best friends with my cousins and brother ffs. She keeps wailing how much she loves him but you don't cheat on those you love.

  What should I do reddit? I almost feel like I should calm her down for now but then call him and tell him. She has no intentions of telling him anytime soon seeing that their wedding is in October. I don't want him to marry someone who fucked him over again, theres no excuse for cheating..(also my bf and I are attending their wedding) I don't wanna be the middleman in this situation, not my relationship to get too involved. I don't wanna speak to her like I do every other cheater ive encountered, but still....she deserves a harsh reality. Help!!
<bot>: friend cheated on her fiancé with ex bf weeks before her wedding. good friends with both of them, not sure what to do now.