To put this into context, DS's father is a very difficult man. I left him years ago due to abuse but he has created problems and conflict ever since.
DS has foootball training at the weekends. He's with his dad EOW so we each take him on our weekends. His dad is one of those men who shout from the sidelines and it puts a lot of pressure on DS to the point where he doesn't even want to go with his dad.
His dad has now decided he would also like to watch him on my weekends. It spoils my enjoyment as I find it very stressful to be around him, but far more importantly it ruins it for DS. In my view, he's also encroaching on my time with DS though you might argue it makes no difference.
He's not the kind of man who will take any notice if I say it would be best all round if he wasn't there. In fact it will make him all the more determined. He also wouldn't listen to DS, not that he would dare be completely honest with him about how he feels.
There have been other instances where he's ruined DS's enjoyment of something to the point where DS would rather not bother and I don't want this to turn out the same.
More of a WWYD than an AIBU.