My 15 year old son leaves tomorrow morning for a week's vacay with his father, his father's girlfriend,and another couple that are long time friends of his father. They are going to visit his father's mom, dad, and grandma.
My son is over the moon excited about this trip and has been looking forward to it all summer.
Me, I just don't like his father's family - there is a lot of backstory - so I have a hard time getting excited for my son. In fact, I would rather he not go on this trip. But, I also recognize that these people (well most of them) are his family also and he has a right to know them and be loved by them. Even if it makes my skin crawl. LOL
All this to say, it gets easier, after a while. Because we want what is best for our children. And to let them know their "other" family is (usually) a good thing. As you move farther away from your divorce your child's interaction with his father will bother you less. My standard is to ensure that his father etc. treat him with respect and love - which, I have come to grudgingly admit, they do.
Ultimately, my son comes home to me. And I know that he loves me and I know that, even at 15, he sees me as the most consistent adult in his life.
Good Luck
God Bless