G.B.
In most situations a child reaches that states designated age and they can go in front of the judge and ask for their visitation to be terminated. My niece went before the judge at age 8 and told him a whole list of reason's she wanted to live with her dad. My sister had done nothing wrong but she was religious and her daughter didn't want to go to that church. The judge sided with the dad and let her dad have full custody.
BUT they judge does NOT have to honor their request. The father has a right to see his child and that judge just can't say he is terminating the visits "just because". He has to give valid reasons that fit into a lawful reason to terminate the court order.
Just because your son doesn't want to see his dad that does not mean the dad loses his rights to see his child. Sometimes kids are kids and they just have to do stuff because it's the right thing to do.
When he's an adult he can choose whether to have his dad in his life or not. But he's a child and YOU need to reinforce he has to go spend time with his dad. YOU have to make it a good thing for him to do.
IF you're telling him you understand he doesn't want to go, you're telling him you don't want him to go. You're telling him to not see his dad.
If you're being very careful and saying things like Your dad loves you honey, you need to spend time with him. Your dad is a great dad and he wants to see you, you need to go and enjoy this time with him, etc...then you're reinforcing he has to go see dad.
Be his parent and tell him you want him to go visit his dad and that's that. Unless he can tell you specific reason's as to why he doesn't want to go then you want him to go and have a good time with his dad.