Your ex isn’t exactly helpful, is he! How old is your son?
what would he like to do? Does he play on-line games Minecraft etc? Does your ex not have internet? Or does your son want to be more sporty – football or cycling? Can he take his bike to his dad’s and they cycle together.
My ex has no imagination so I organised things for when they are together. My ex has our son on Sundays so I organised a karate class. Ex needs to get him there, can sit and watch, or join in, and take him home. son is not bored.
or I’d send son along with project from school – the last topic was Mexico and they had to make some Mexican food so I sent a recipe for enchiladas. They shopped for ingredients, made the food between them and had to take photos.
it takes some planning and I get annoyed that ex is so bone idle he won’t make the effort, but I’d rather my son was happy