I had a similar experience. My best friend of 17 years slept with my fiance. They both regreted it and were truely sorry. I forgave my fiance quite fast but her on the other hand it took me over 2 years to even talk to her. When i finally chose to have her in my life again i made it loud and clear that the friendship was gonna be on my terms. She bent over backwards to make sure i was one hundred percent comfortable. My fiance hated the fact i was talking to her again but he understood it wasnt his descision. Long story short its been 8 years since it happened i couldnt be more happy with my husband and i still talk to my friend. We will never be as close as we were before and shes fully aware of that and ok with it. Hope everything works out for you and remember everything should be done on your terms!

Hope this helps