This has been a constant battle with H and Ss and I. They don't want OW at their sporting events and I don't want here there either. But H sees nothing wrong with it and she has attended since they began seeing each other. Everyone knows we were once friends and it just makes her look bad. Now the boys are in college and the football stadium is much bigger. I don't even have to see her there. I hope your H respects your wishes without a fight.
Everything happens for a reason, maybe Dad needs to find that it isn't better out there, he needs to realize how good he had it here. Maybe he will find God and that is the most important thing when he finds Him he will know he is supposed to come home.