Scout, may I offer a different perspective? This doesn't turn on whether it was right or wrong for him to have asked or whether it is your responsibility. I personally would rather be the one to transport my child 1/2 hour by car than rely on unnamed others, arranged by a flaky ex-husband to do so. While I know you have lots and lots of time with S2, as the parent of one child in college and another soon to be, I can tell you that the times we spent in the car driving places were some of the best times we spent talking, laughing, singing, playing I spy, you name it. Forget about your Ex. Always, in every case, do what is best for S2. Let that be your driving force and the consideration that dictates your actions.
I totally second that. Every single part of it. And add to that that nothing that you do is going to teach your H or his family to see things rightly. Just be the light to your kid.
I believe I will see the bounty of the Lord in the land of the living. Wait for the Lord with courage. Be stouthearted, and wait for the Lord.