Maid of Honor Help!

My best friend and I met when I was 3 and she was 4. We remained best friends up until a couple of years ago. How we met at such a young age was my sister was dating her uncle and they eventually had my niece and got married, then moved a few hours away, and had my nephew. Well a couple of years ago while my sister and her kids lived a couple hours away, my brother-in-law (bestie's uncle) moved back to our home town to look for work and my sister and kids still lived a couple hours away. While my brother-in-law was looking for work, he started cheating on my sister with his high school gf. He would bring this gf around his mom's house and his family, including his niece which was my best friend. His niece, my bff, knew this affair was going on and did not say anything to me or my sister. Once my sister found out about the affair I confronted my bff and she said she didn't want to get involved because that's her uncle, which I can understand, but as someone who has been there for my bff when she was cheated on and she was there for me when I was cheated on in the past, you would think as a women she would not want to see that happen to anyone and at least give me or my sister a hint or subtle heads up. She had no remorse and is now really close to my ex brother-in-law and (now) his new wife. It had definitely put a wedge in our friendship over the last couple of years and we have barely seen or spoke to each other except for birthdays and a few random times throughout the years. But she was always supposed to be my maid of honor growing up and now I have no female friends ( other than relatives like my sister and sister-in-law and cousins) I have ever been as close with prior to all the drama. What do I do?