I have been co parenting my 6 year old autistic son somewhat successfully with my ex for over a year now until christmas day when my son told me about an sa that happened to him by his fathers friend while he was staying at his fathers house, the police couldnt take it any further for lack of evidence and because of my sons lack of communication skills with him being autistic and only 6, i am now terrified to send him back to his dads house for visits or overnight stays, especially since his dad refused to believe it and has not agreed to keep the friend away, i believe my sons allegation is true but his dad wont believe it and at times actively goes against my wishes on certain things to do with the care of my son. Because he doesn't believe and because in the past my ex has lied to me about things that have happened regarding things iv asked him not to do im now terrified to send my son to his dads for visits or stays, i dont want to put him in the same position again, i fully belive his dad would tell me the friend isnt around when he is.
What would be the best way to deal with this and keep my son safe