I'll say again what I have said to you before.
By getting so upset, being hypervigilant about son's time at dads house, interrogating son about his time at dads, pumping your son to dislike his stepmom, YOU are hurting your child. You are putting your child in the middle of your conflict with dad. Do you want to raise a healthy, well-adjusted child? Stop putting conflict in his life. Get a therapist...vent to the therapist. You REALLY need support.
Are there any parenting classes where you live? Many places now offer parenting classes on how to parent with an ex. What about taking a coparenting class with dad? If you are who I remember, and your ex is who I remember, my take is he doesn't want the conflict...he just wants to live his life, be a good father, and move on. I suspect if you and dad did some coparent counseling together, or a class, you might be suprised at his willingness to discuss (vs being dictated to) parenting issues. If you keep focused on the conflict, it will always be there for your son. I promise.
Also you are putting your son 'in the middle' by asserting your rules on him at his dads house. Stop being pushy and demanding. IF you continue having concerns (and no helmet does NOT rise to the level...nor does paranoia about step mom being a molester), ask for a GAL.
(sorry folks...I'm sure some of you are disappointed....just a tiny tiny hope mom will get this is not about her)