My Dsis seperated from her exH 4 years ago. It was awful, he was emotionally, financially and at the end physically abusive to her. The fall out has been horrible, her exH has never had the balls to face me or any of my family since then. He left her in a terrible position financially and mentally, which she is only just now starting to get out of. There are no DC's involved.
Our cousin (female) was around at the time of the break up, and saw what a mess Dsis was in, she, Dsis, was suicidal
Cousin moved to the other end of the country shortly afterwards and has not been back to our home town since then. Backstory is that Cousin is toxic, has lied and manipulated in the past. The reason she left our home town is that she had an affair with a married man (not the exH) got found out and had to get away sharpish.
She (Cousin) is coming to visit family next week, and has told my DM that she intends to visit the exH, as she "Feels sorry for him" She is not planning to see my Dsis but has asked to come and see me.
AIBU to say no, she is not welcome at my home if she is going to engage with that bell-end, who by the way is very nicely set up now, new partner, new home, new family, while Dsis is still struggling with the fall out that he left behind.
My DM (Not Dsis Mum - it's complicated) thinks that I am being childish and that it's all water under the bridge. I, on the other had think that it will be a massive betrayal to my Dsis if I engage with the Cousin. I have not spoken to Cousin for over 3 years, and tbh it's not been any loss at all.
None of us have had any kind of relationship with her (Cousin) while she has been away - her choice BTW not ours. But my DM will create a fuss and may try to force the issue, I can fully imagine her just turning up with Cousin at my door, which I have told her not to do as I will then just turn them away.
So, AIBU and childish? Or loyal to my Dsis?