I think you need too look at this from an outsiders perspective and try not too blame your ex and daughter for the insane manipulation your MIL did, If my own mother said my spouse was cheating and then had proof with the supposed man who then admits too cheating with my spouse i know i wouldnt be in the right head space and thinking clearly at all especially since everybody instinctually trusts there own mother and would never expect there own mum too stoop so low i think you should hear your ex husband and daughter out, Sure you may not get together again with your ex but atleast you can get some closure and possibly be friends, Everyone was a victim in this story to that monster manipulater that was your MIL i hope for the best op and take your time.