Ex DH and I divorced 8 years ago when DS was 8 because Ex DH had an affair.
Ex DH is and always has been a great father, but the divorce has always effected how DS has treated him over the years.
When Ex DH introduced him to his now SM, (same woman he was having an affair with) DS was utterly horrid to her and then simply tolerated her over the years. He's never invited SM or her 2 children, his half siblings to anything, doesn't speak about them unless it's to mock them and tends to just stay in his room glued to his phone until he's forced to join in with them.
He is unfortunately the step child from hell. E.G when they took him away on a trip to America, he was very vocal about not wanting to go but then he's always vocal about doing anything with them. He went out of his way to make everyone miserable, complained about everything, disliked everything etc
When he was introduced to my new DH when he was 10 he was a little angel and continues to be so for new DH.
He's always asked new DH to do things with him that would have been more appropriate to ask his dad to do, ex DH always tagged along without a single complaint.
We don't live too far from each other, so DS started travelling alone at aged 12, he goes to his dad's Friday after school and comes home Sunday night and on holidays they tend to have him for the whole time except Christmas where we alternate and Summer we split, 3 week with each of us.
2 years ago, DS started complaining that he was never free on weekends because he was stuck at his Dads, who always wanted to drag him to do things together. I told him to suck it up and go and that he was lucky to have a Dad who loved to do things with him. Which is probably the only nice thing I've ever said about Ex DH to him.
He kept up with the visits but over the past few months he's slowly began cutting back on them, he's 16 now and I've demanded he go and only after a lot of back talk will he actually do it.
Ex DH suggested if the weekend visits were no longer to his liking, they could meet up once or twice during the week to do something together but DS has blown him off on numerous occasions and when dragged there, his behaviour is down right rude.
I honestly don't think I can do anything more but I do know that over the years I could have done far more to help their relationship but have chosen to just opt out as it didn't directly effect my relationship with my DS, so I'm feeling guilty.