First post so sorry if I don't get all of the abbreviations just right.  I have a 13yo S, and my fiancé has 12yo D and 16yo S from his previous marriage.  We got engaged in 2018 and his D absolutely lost it (not sure why as her mom had already remarried a year prior and they had been split for 3 years at that time).  When she realized that tears wouldn't get him to call off the engagement she started making up lies about my son (he's not perfect but these were very out of character for him).  These escalated until they reached a point where she is no longer allowed to visit because I feared for my sons safety and future.  My fiancé agreed that these weren't things my son would say/do and that it was in everyone's best interest to keep her away from our home and my child.  So we go and visit her for a day here and there, but the time is definitely less than it was.

We're supposed to get married at the end of this year and of course we want our kids to be there.  We're working on trying to get them around each other over the summer to make sure they can handle it for the wedding.

Fiance and his ex are just ready to let bygones be bygones and not have any serious discussions, and let her start coming over for visits.  I feel like everything is just being swept under the rug and for my sons safety I don't feel ok with that at all.  I can't speak to his ex, she's self righteous and refuses to have an honest conversation "my children are my world" "my children never lie" "my children are godly and I'm a good mother".  I don't really know what I hope to gain from this, and I don't feel like there will ever be closure, but I'm really struggling to let things move forward...

Fiancé always listens but he doesn't know what else to do or how to help.

Thanks for letting me vent.