Yep I've thought those same thoughts about my husband "I'm not his momma."
Why do we think that? Mine lived with his mom until I met him (he was 26) and she cooked his meals, did his laundry and made his bed. He still calls her almost daily and she lives 6 miles down the street. I don't mind as much now as I use to. Mostly because he is a good husband, works very hard, and is he is very loyal. He also takes care of me a great deal. But part of it is because my own mom passed away and I've realized that time is short and we all deserve to feel loved. So it's a give and take relationship.
But yes, when it comes to health, there is only so much we can do. Educate and share our information. Everyone has free will and that's how it should be. You may hate to see him swallow that statin everyday, but it is his choice. And it can be a harder pill for you to swallow - in watching him so soon after his heart attack, taking those meds, and wondering if he is just making his health worse.
After reading your post I decided my husband should probably go back to taking COQ10. He took it while taking the statin, but then stopped for a while once he got off of the statins.
I love that serenity prayer! It has gotten me through some hard times.