Being a good father to your son and being in his life does not mean you're only thinking of you and not your son. That's silly. He needs you and it will not be easier on him to not have you around.
Visual fixations... hmmmm. i read somewhere that watching a fish tank full of fish is calming for those with visual fixations. You can tell S that you'd like to take him to pick out a friend that he can visit at dad's house and get a beta fish. Let him name the fish and every time you see him tell him that the fish misses him and can't wait to see his face, etc.
If he likes music, introduce him to some fun music in the car. My daughter LOVES music and it all started with Michael Jackson.
These are sensory things to help him associate being with daddy as soothing and a good time. The transition part is probably hard, leaving mommy going to daddy... this is where mantras work well with children with Autism. Say the same thing over and over every time during this transition. Something like, "Mommy will be in your heart while you're at daddy's" and when you take him back to mommy's house say, "daddy will be in your heart while you're at mommy's" Sometimes this takes a few months but it really works. It always has to be said calmly and in a soothing tone, almost whispering in his ear while you're touching him.
This process is hard on ALL children but children on the spectrum have an extra set of challenges. Good luck and keep us posted.
